Article

The Sequestration, Processing and Retention of HoneyBee Promelittin Made in Amphibian Oocytes

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Abstract

Messenger RNAs from one kind of secretory cell can be introduced into the cytoplasm of another: the heterologous proteins formed by the recipient cell are usually processed and topologically segregated in the manner characteristic of the donor cell. Xenopus oocytes injected with honey-bee venom gland RNA provide some support for this generalization, but also reveal important exceptions to it. Thus, the frog cell makes a small polypeptide whose partial sequence matches perfectly that of insect promelittin, except that the product formed in oocytes ends at the C terminus with a glycine as opposed to a glutamine amide residue. N-terminal heterogeneity is seen in protoxin made in oocytes and venom gland cells, and species shorter by two residues are seen in both tissues. We suggest that the oocyte contains a dipeptidylpeptidase. Promelittin made in oocytes is barely detectable in the cytosol but is found associated with a vesicle fraction which also contains some newly synthesized endogenous oocyte proteins. The association with vesicles is long-lasting; thus promelittin is retained slightly more efficiently than sequestered oocyte proteins, and an incubation period of about two weeks is required to reduce by half the amount of these endogenous vesicle proteins. Thus neither promelittin nor any products derived from it are secreted rapidly. Gel analysis fails to reveal promelittin in the medium surrounding the oocyte, although traces can be detected by assaying for a characteristic heptapeptide. Such small amounts could result from slow secretion or leakage. Melittin could not be detected by gel analysis or peptide assay. The retention of the honey-bee protein within the frog cell is discussed in terms of the specificity of the processing systems and secretory pathways of venom gland cells and oocytes. We suggest that whilst some export mechanisms function efficiently in a wide variety of cells, others do not, and may even be restricted to specific cell types.

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... Animal mRNAs are also translated in Xenopus oocytes as well as mRNAs for secretory proteins from Dictyostelium discodium and a wide variety of viral proteins (10,26,42). Post-translational processing of both plant and animals proteins has been demonstrated (1,23,25,34) and zein proteins have been shown to be compartmentalized within the membrane vesicles of oocytes (16). ...
... Even if wheat a-amylase were glycosylated at the level seen for the barley protein, we would probably not detect the 290-dalton difference with our gel system. Lane et al. (8,23) have shown that oocytes programmed with heterologous RNA from secretory proteins are able to translate, process, and secrete these proteins into the incubation medium. ...
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... In fact the fidelity of this aspect of the post-translation processing by oocytes appears extremely high, with several foreign non-secretory mutant proteins exhibiting a similar phenotype when tested in oocytes (Table 1). One exception to this generalization is bee venom promellitin which is not significantly exported from oocytes (Lane et al., 1981~). In this case the incomplete processing and hydrophobicity of the molecule may impede its translocation. ...
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RNA aus Harding-Passey-Melanomzellen wird mit Hilfe von Mikroglaskanülen in Muskelzellen injiziert und der Einbau von [3H]l-DOPA als Vorstufe des Melanins autoradiographisch untersucht. Ein Einbau von l-DOPA in den Muskelzellen konnte nur nach der Injektion von Melanomzellen-RNA erreicht werden. RNA aus Rattenleberzellen und Ribonuclease-behandelte Melanomzellen-RNA bewirken nach Injektion in die Muskelzellen keinen Einbau von l-DOPA. Dagegen beeinflußt eine Desoxyribonuclease- und Pronasebehandlung der Melanomzellen-RNA nicht die Ergebnisse. Cycloheximid verhindert den Einbau von l-DOPA sowohl in HARDiNG-PASSEY-Melanomzellen als auch in Muskelzellen nach Injektion von Melanomzellen-RNA.
Article
Melittin, das toxische Haupt-peptid aus Bienengift, besitzt folgende Primärstruktur: Gly-Ile-Gly-Ala-Val-Leu-Lys-Val-Leu-Thr-Thr-Gly-Leu-Pro-Ala-Leu-Ile-Ser-Trp-Ile-Lys-Arg-Lys-Arg-GlNGlNNH2. Sie ergibt sich aus der Analyse der tryptischen und peptischen Spaltstücke sowie dem partiellen Abbau des Gesamtpeptids nach Edman. In geringer Menge auftretende Fragmente weisen auf die Existenz von Begleitstoffen in manchen Melittinfraktionen hin, die Nterminal in noch unbekannter Weise substituiert sind und/oder sich in wenigen Aminosäureresten unterscheiden. Das Bauprinzip des Melittinmoleküls besteht in der extrem ungleichmäßigen Verteilung vorwiegend hydrophober, neutraler (Pos. 1-20) und hydrophiler, meist basischer (21-26) Aminosäurereste. Die pharmakologischen und biochemischen Effekte des Melittins hängen mit seinem Tensidcharakter zusammen; dieser ergibt sich aus der Primärstruktur. Melittin ist demnach das erste Peptid, dessen biologische Wirkung auf Grund seiner Primärstruktur verstanden werden kann.
Article
After feeding labelled leucine to worker and queen bees of different age, the synthesis of melittin and its precursor promelittin in the venom gland has been analyzed. Marked changes in the synthesis of promelittin and the rate of its conversion to melittin occur during the maturation of the insects. In queen bees, both processes operate already close to full capacity in the newly emerged animal. On the other hand, in worker bees the production of promelittin increases slowly to reach a maximum at the 8th to 10th day and then decreases. During the first two days only promelittin synthesis was observed, whereas conversion to melittin was detectable only later on.
Article
Fertilised eggs of Xenopus laevis were injected with rabbit or mouse globin mRNA and allowed to develop. At various times after hatching they were dissected and different regions incubated with radioactive histidine. Two main regions were studied: the yolky endoderm plus ventral mesoderm, and the axial region containing functional myotomes, nerve cord, and notochord. Both regions synthesized the globin appropriate to the source of the injected mRNA and globin synthesis represented a similar proportion of total protein synthesis in each part. The ratio of α to β globin synthesis was not affected by the region of the embryo in which injected mRNA was translated. We conclude that the injected mRNA was evenly distributed in the developing embryos and was translated efficiently in differentiating tissues with no erythropoietic function.
Article
Infrared and radio observations of the galactic core are reviewed with particular attention to the central parsec of the Galaxy. Observations of the Ne II and H II regions in Sagittarius A West are discussed in some detail. Possible explainations of the uniformly low level of ionization in the region of the central parsec are considered. It is maintained that the peculiarities of ionization states observed in this region are most consistent with a model based on the existence of a massive black hole in the galactic center, possibly the compact radio object (diameter less than .001 arcsec) located in IRS-16 in Sagittarius A West.
Article
Translocation of intracellular glutathione to the medium was studied in lymphoid cells (grown in tissue culture) that have very high, very low, or intermediate levels of membrane-bound gamma-glutamyl transpeptidase, in the absence and presence of various inhibitors of this enzyme. The data show that glutathione is translocated to the medium by all of the cell lines studied, but that glutathione does not accumulate in the medium unless the cellular transpeptidase activity is either very low or substantially inhibited. Translocation of glutathione does not seem to be directly related to the activity of gamma-glutamyl transpeptidase. The present and previous [Griffith, O.W. & Meister, A. (1979) Proc. Natl. Acad. Sci. USA 76, 268--272] findings suggest that translocation of intracellular glutathione is a general property of many mammalian cells. Glutathione exported from cells that have membrane-bound transpeptidase may be recovered by the cell in the form of transpeptidation or degradation products. Translocation of glutathione may also reflect operation of a rather general mechanism that protects and maintains the integrity of cell membranes.
Article
The precursor of bovine proparathyroid hormone was synthesized by translation of parathyroid mRNA in a wheat-germ cell-free system. The amino acid sequence of the NH2-terminal extension (the pre sequence) was determined by repetitive Edman degradation of the polypeptide labeled with radioactive amino acids (radiosequencing). The pre sequence of pre-proparathyroid hormone is (formula: see text) which is followed by the sequence of proparathyroid hormone. It is significant that 20 of the 25 amino acids in the sequence are hydrophobic. This high hydrophobicity is consistent with the proposed role of the pre sequence as a membrane-penetrating peptide. The precursor-specific sequence of 31 amino acids was snythesized chemically by the solid-phase technique. This synthetic peptide was shown to bind to the microsomal fraction of homogenates prepared from extracts of parathyroid glands, a finding consistent with the proposed role of the precursor peptide in the attachment of the nascent chain--mRNA--ribosome complex to the endoplasmic reticulum.
Article
Polyadenylated mRNA isolated from mineral oil-induced plasmacytoma (MOPC)-321 was injected into Xenopus laevis oocytes that were incubated in 3H-labeled amino acids. The MOPC-321 k chain was purified from an oocyte homogenate by immunoprecipitation, followed by preparative gel electrophoresis. To determine whether the precursor segment had been properly and precisely cleaved in the oocyte, the amino acid sequence of the NH2terminal end of the purified k chain was investigated. The NH2-terminal sequence obtained was identical to that of the mature, secreted form of the protein. Thus the specificity of the enzyme performing the cleavage of precursor to mature chain is similar in frog oocytes and in mammalian cells. Therefore, the enzymatic specificity has been highly conserved during evolution and evidently performs an essential role in cellular metabolism.
Article
Melittin messenger RNA from queen bee venom glands has been translated in a cell-free system from wheat germ. A product larger than promelittin is formed which has the carboxy-terminal sequence-Gln-Gln-GlyCOOH. Melittin and promelittin from venom glands terminate in -Gln-GlnCONH2. The possible role of the extra glycine residue in the formation of a COOH-terminal amide via a transamidase-like reaction is discussed.
Article
Translation of melittin messenger RNA from queen bee venom glands in a cell-free system from wheat germ yielded prepromelittin. Sequence analysis of the labeled in vitro product was performed by automatic Edman degradation of the intact polypeptide as well as by analysis of some of its proteolytic fragments. Prepromelittin was shown to be composed of 70 amino acids, two of which have not been identified. The sequence of melittin is located in the COOH-terminal third of the polypeptide chain (residues 44--69). Prepromelittin starts with a very hydrophobic pre-region, probably 21 residues long, followed by a pro-part of unusual sequence, containing only alanine, proline, and acidic residues. At least three post-translational reactions are required to convert prepromelittin to mellitin.
Article
We have used direct microinjection of messenger RNA into individual mouse and human cells to assay for specific translation products. We have been able to detect the synthesis of human fibroblast interferon, thymidine, kinase, hypoxanthine phosphoribosyltransferase, adenine phosphoribosyltransferase, and propionyl-CoA carboxylase in response to injected mRNA. Using the interferon system as a model, we have quantitated interferon synthesis and followed partial purification of interferon mRNA sequences on sucrose density gradients. The methods we have utilized should be applicable to other systems in which sensitive assays exist for gene products and should provide a screening procedure for isolating specific mRNA sequences.
Article
When human lymphoblastoid mRNA was microinjected into X. laevis oocytes, titers of interferon rapidly reached a maximum inside the oocyte while accumulation of interferon continued in the incubation medium for at least 45 hr. If interferon protein was injected into oocytes it was rapidly inactivated. Significantly, newly synthesized interferon but not injected interferon was found to be membrane-associated. Further experiments involving the co-injection of mRNAs coding for secretory proteins (guinea pig milk proteins and human interferon) and nonsecretory proteins (rabbit globin) revealed that only the secretory proteins were exported from the oocyte. Moreover, different proteins were exported at different rates. A distinct subclass of newly synthesized oocyte proteins of unknown function also accumulated in the incubation medium. Since the information encoded in the messenger RNAs of secretory proteins is sufficient to specify synthesis, compartmentation and secretion of these proteins, the oocyte may provide a complete system for the analysis of the secretory process.
Article
The stability and distribution of proteins within the living cell can be studied using Xenopus laevis oocytes. Microinjection of messenger RNAs and secretory proteins, followed by cell fractionation, shows that transfer of ovalbumin and milk proteins across intracellular membranes of the oocyte only occurs during their synthesis. Thus milk protein primary translation products, made in the wheat germ cell-free system, when injected into oocytes remain in the cytosol and are not recovered within membrane vesicles. Such miscompartmentalized primary milk proteins are rapidly degraded (t1/2 0.6 ± 0.1 h). In contrast, processed milk proteins, extracted from oocytes injected with mammary gland RNA, are relatively stable when introduced into the cytosolic compartment (t1/2α-lactal-bumin 20 ± 8 h, casein A 6 h, casein B 4 h, casein C 8.3 h). The primary ovalbumin product is also stable (t1/2 22 ± 9 h). Indirect evidence that rapid degradation of miscompartmentalized milk protein primary translation products may occur in vivo was obtained by the injection of massive amounts of ovalbumin and milk protein mRNA. Under these conditions there is no accumulation of primary milk protein translation products, but a polypeptide resembling the unglycosylated ovalbumin wheat germ primary product can be detected in the cytosol. Only the glycosylated forms of ovalbumin are found in the oocyte membrane vesicle fraction. We discuss the roles played by the presence of detachable signal sequences and the absence of secondary modifications in determining the rate of degradation of primary translation products within the cytosol.
Article
The Xenopus oocyte can be used to study the nature and specificity of the translational and post-translational systems of a normal living cell. We describe experiments combining messenger RNA microinjection and subcellular fractionation. Total Xenopus liver RNA directs the synthesis of albumin and vitellogenin contained within membrane vesicles; similarly, guinea pig mammary gland mRNA codes for membrane-bound protease-resistant milk proteins. In contrast, iodinated albumin protein injected into oocytes remains in the supernatant fraction, as does globin made on mRNA. The information encoded in the albumin messenger is therefore sufficient to specify synthesis of a membrane-bound product; moreoever, this highly efficient coupled translation-processing system may be of use in the study of the transfer of newly made proteins across membranes. A significant proportion (up to 20%) of newly made oocyte proteins enter a light membrane fraction, and many remain there. We speculate that these vesicles represent part of an important storage system.
Article
Total poly(A)-containing RNA from Brockmann boides of carp (Cyprinus carpio) directs the synthesis of authentic carp proinsulin in Xenopus oocytes. Neither preproinsulin nor further processing of the proinsulin to insulin can be detected in the oocytes.
Article
Prepromelittin, obtained by translation of melittin mRNA in a cell-free system from wheat germ, was incubated with subcellular fractions from rat liver in the presence of deoxycholate. The product formed had the same amino terminal sequence as honeybee promelittin. The processing activity was membrane-bound and was shown to reside in both microsomal and mitochondrial/lysosomal fractions from rat liver.
Article
The data presented in this paper demonstrate that native small ribosomal subunits from reticulocytes (containing initiation factors) and large ribosomal subunits derived from free polysomes of reticulocytes by the puromycin-KCl procedures can function with stripped microsomes derived from dog pancreas rough microsomes in a protein-synthesizing system in vitro in response to added IgG light chain mRNA so as to segregate the translation product in a proteolysis-resistant space. No such segregation took place for the translation product of globin mRNA. In addition to their ability to segregate the translation product of a specific heterologous mRNA, native dog pancreas rough microsomes as well as derived stripped microsomes were able to proteolytically process the larger, primary translation product in an apparently correct manner, as evidenced by the identical mol wt of the segregated translation product and the authentic secreted light chain. Segregation as well as proteolytic processing by native and stripped microsomes occurred only during ongoing translation but not after completion of translation. Attempts to solubilize the proteolytic processing activity, presumably localized in the microsomal membrane by detergent treatment, and to achieve proteolytic processing of the completed light chain precursor protein failed. Taken together, these results establish unequivocally that the information for segregation of a translation product is encoded in the mRNA itself, not in the protein-synthesizing apparatus; this provides strong evidence in support of the signal hypothesis.
Article
Dipeptidyl peptidase IV, an enzyme that releases dipeptides from substrates with N-terminal sequences of the forms X-Pro-Y or X-Ala-Y, was purified 300-fold from pig kidney cortex. The kidney is the main source of the enzyme, where it is one of the major microvillus-membrane proteins. Several other tissues contained demonstrable activity against the usual assay substrate glycylproline 2-naphthylamide. In the small intestine this activity was greatly enriched in the microvillus fraction. In all tissues examined, the activity was extremely sensitive to inhibition by di-isopropyl phosphorofluoridate (Dip-F), but relatively resistant to inhibition by phenylmethylsulphonyl fluoride. It is a serine proteinase which may be covalently labelled with [32P]Dip-F, and is the only enzyme of this class in the microvillus membrane. The apparent subunit mol.wt. estimated by sodium dodecyl-sulphate/polyacrylamide-gel electrophoresis and by titration with [32P]Dip-F was 130 000. Gel-filtration and sedimentation-equilibrium methods gave values in the region of 280 000, which is consistent with a dimeric structure, a conclusion supported by electron micrographs of the purified enzyme. Among other well-characterized serine proteinases, this enzyme is unique in its membrane location and its large subunit size. Investigation of the mode of attack of the peptidase on oligopeptides revealed that it could hydrolyse certain N-blocked peptides, e.g. Z-Gly-Pro-Leu-Gly-Pro. In this respect it is acting as an endopeptidase and as such may merit reclassification and renaming as microvillus-membrane serine peptidase.
Article
Xenopus liver vitellogenin and albumin mRNAs injected into Xenopus oocytes are correctly translated, as shown by specific immunoprecipitation and co-electrophoresis with purified Xenopus vitellogenin (molecular weight 210,000 daltons) and albumin (molecular weight 72,000 daltons). Vitellogenin made in oocytes under the direction of injected liver mRNA is unstable compared to other proteins made on injected messengers (such as albumin and globin) and endogenous oocyte proteins (including actin), the half-life of newly made vitellogenin being about 8 hr. Pulse-chase experiments with 35S-methionine show vitellogenin to be a precursor to yolk platelet lipovitellin (molecular weight 120,000 daltons), while 3H-serine labeling demonstrates conversion to phosvitin (molecular weight 34,000 daltons). In contrast, injected 3H-serine 35S-methionine-labeled Xenopus vitellogenin protein is not converted to yolk platelet proteins and is degraded rather slowly (half-life, 23–29 hr).
Article
Venom glands of honeybees synthesize the peptide melittin via the precursor promelittin. Total RNA preparations from venom glands served as template in a cell-free system prepared from mammalian cells. The heterologous system translated the insect mRNA with approximately the same efficiency as hemoglobin mRNA. A polypeptide was synthesized which, as shown by acrylamide gel electrophoresis in the presence of detergent, has a higher molecular weight than promelittin. Analysis of peptic fragments as well as Edman degradation have demonstrated that sequences characteristic of venom gland promelittin are present in this product formed in vitro. Furthermore, a bacterial protease which specifically splits after acidic residues liberates from the cell-free product a fragment which closely resembles melittin. Evidence is presented that most of the extra amino acids are located at the amino terminus of the product formed in vitro. The larger polypeptide detected in vitro may represent a precursor of promelittin.
Article
The sizes of amino acid pools in developing oocytes at various stages have been determined for normal and for human chorionic gonadotropin (HCG)-stimulated Xenopus laevis. The total amino acid pool increases 20- to 30-fold in oocytes in stages II through V. This increase is commensurate with the increase in size of the oocyte. In addition, the pool is greater (5% in stage II and 29 to 38% in stages III through V) in oocytes from the HCG-stimulated frogs. Glutamic acid accounts for approximately 35–45% of the total amino acid pool in all stages of oocytes. In none of the stages, however, are there detectable amounts of either proline or cysteine.
Article
Venom glands of young queen bees (Apis mellifera) synthesize the toxic peptide melittin as their main product. Melittin is formed by proteolytic cleavage of a precursor, promelittin. Unfractionated RNA prepared from venom glands was injected into Xenopus oocytes and was shown to direct the synthesis of a promelittin-like substance. About half of the peptide chain made in oocytes has been sequenced; the 17 amino acid residues identified correspond exactly with sequences found in promelittin from venom gland cells. These results yield final proof that injected messenger RNAs can be read with great fidelity. The translation of a messenger from an insect gland shows that at least some of the translational systems within the oocyte are neither cell-type nor phylum specific. It seems likely that the oocyte can be used to assay any kind of eukaryotic mRNA.The conversion of promelittin to melittin could not be detected in oocytes. Moreover, the promelittin synthesized in oocytes differs at the carboxyl end from the product made in gland cells, for the latter terminates with glutamine amide while the oocyte material probably ends with an amino acid with a free α-carboxyl group. Some of the post-translational modifications characteristic of gland cells thus do not seem to take place in oocytes.
Article
Rabbit or mouse globin mRNA was injected into fertilized eggs of Xenopus laevis. Of the injected eggs, 30% survived to the swimming tadpole stage, and 15% became frogs. Sephadex and carboxymethyl cellulose chromatography was used to show that rabbit or mouse globin was synthesized continuously by embryos and tadpoles up to the stage when feeding commenced (c. 8 days after fertilisation). The rate of protein synthesis rises greatly during development, but the rate of rabbit or mouse globin synthesis in frog embryos remains approximately constant for at least 8 days of development, during which about 20 cycles of cell division take place. For mouse haemoglobin mRNA, the ratio of α to β globin synthesis does not change during this period. We conclude that injected globin mRNAs are stable during development.
Article
RNA from tobacco mosaic virus can be translated inside oocytes of the frog Xenopus laevis. The main product is a polypeptide with a molecular weight of 140,000. There is no evidence for coat protein synthesis, and it is unlikely that the polypeptide that is made contains either a whole or a partial coat protein sequence. The picture of translation of tobacco mosaic virus RNA obtained using oocytes is very much simpler than that found using cell-free protein-synthesizing systems, in which a great many polypeptides are made under the direction of tobacco mosaic virus RNA. The reasons for this difference are discussed, and the relative merits of in vivo and in vitro protein-synthesizing systems are compared.
Article
A simple method is described for detecting 3H in polyacrylamide gels by scintillation autography (fluorography) using X-ray film. The gel is dehydrated in dimethyl sulphoxide, soaked in a solution of 2,5-diphenyloxazole (PPO) in dimethylsulphoxide, dried and exposed to RP Royal “X-Omat” film at -70 °C. Optimal conditions for each step are described. β-particles from 3H interact with the 2,5-diphenyloxazole emitting light which causes local blackening of an X-ray film. The image produced resembles that obtained by conventional autoradiography of isotopes with higher emission energies such as 14C. 3000 dis. 3H/min in a band in a gel can be detected in a 24-h exposure. Similarly 500 dis./min can be detected in one week. When applied to the detection of 35S and 14C in polyacrylamide gels, this method is ten times more sensitive than conventional autoradiography. 130 dis. 35S or 14C/min in a band in a gel can be detected in 24 h.
Article
The biosynthesis of melittin, the main toxin of bee venom, was studied in vivo by feeding radioactive amino acids to honey bees. Extracts from venom glands were analyzed for the presence of labelled melittin and other components. Radioactivity was first incorporated into another peptide which is considered to be a precursor of melittin. This conclusion is based on the observed labelling kinetics demonstrating the transient formation of this peptide. Furthermore, the structural similarity between melittin and this component could be established. Evidence is presented showing that it differs from melittin at the amino end. The precusor peptide could not be detected in the ejected venom.
Article
A detailed, computerized procedure for analysing the translocation process of any protein with known sequence from a physico-chemical point of view is presented and used to gain a better understanding of the molecular 'rules' that govern the final outcome of the process. With the aid of this prodedure a number of testable predictions of the orientations of particular membrane-bound proteins can be made. It is also suggested that ovalbumin, the only known secreted protein lacking a cleavable prepiece, initiates translocation in a way that differs from other secreted proteins.
Article
Melittin, the main constituent of honeybee venom, is derived from promelittin. In the amino acid sequence of the 'pro' region of this precursor, every second residue is either proline or alanine. The possibility has been investigated that activation of promellitin might proceed via sequential liberation of dipeptides catalyzed by a dipeptidylpeptidase IV. As substrates we used promelittin isolated from queen bees fed with radioactive proline, and enzymatic fragments of prepromelittin which contained the entire pro part and the NH2-terminal hexapeptide of melittin. It could first be demonstrated that pig kidney of dipeptidyleptides catalyzed by a dipeptidylpeptidase IV. As substrates we used promelittin isolated from queen bees fed with radioactive proline, and enzymatic fragments of prepromelittin which contained the entire pro part and the NH2-terminal hexapeptide of melittin. It could first be demonstrated that pig kidney of dipeptidylpeptidase IV releases dipeptides from the pro part. An enzyme of this type could then be detected in extracts from venom glands of q bees, which also contain a dipeptidase. After inhibiting the latter enzyme with mersalyl, a stepwise cleavage of dipeptides, starting at the amino end of the pro region could be demonstrated. This hydrolysis did not proceed into the melittin sequence. Furthermore, fragments with an extra residue at the amino end, which therefore had the wrong 'reading frame' for the dipeptidylpeptidase, were not hydrolyzed. With intact promelittin as substrate the rate of hydrolysis was always lower than with the fragments. The results presented in this paper suggest a new type of precursor-product conversion proceeding via stepwise cleavage of dipeptide units. Our experimental evidence also ascribes a biological function to a dipeptidylpeptidase IV, a type of enzyme widely distributed in animals tissues. The evidence, that the observed reaction in vitro reflects the mechanism of promelittin activation in vivo is discussed.
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Institut fur Molekularhiologie der osterreichischen Akademie der Wissenschaften
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L. Haiml and G. Kreil, Institut fur Molekularhiologie der osterreichischen Akademie der Wissenschaften, BillrothstraDe 11, A-5020 Salzhurg, Austria
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Jilka, R., Familletti, P. & Pestka, S. (1979) Arch. Biochem. Biophys. 192,290-295.
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Laboratory of Developmental Biochemistry, National Institute for Medical Research of the Medical Research Council, The Ridgeway
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C. D. Lane and J. Champion, Laboratory of Developmental Biochemistry, National Institute for Medical Research of the Medical Research Council, The Ridgeway, Mill Hill, London, Great Britain, NW7 1AA
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