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    ABSTRACT: It is generally accepted that the lysosomal compartment plays an important role in the degradation of cellular components. In this communication we discuss various experimental models which have been used to study mechanisms of intralysosomal degradation and also discuss the evidence obtained in support of the following proposals: 1. The autophagosomes can be isolated into high purity and are the subcellular locus of induced protein degradation. 2. Different membrane components such as proteins and lipids are degraded at different rates inside the lysosomes. Intralysosomal hydrolysis is not the rate limiting step in degradation. 3. Lysosomes take up soluble material in vitro by invagination and pinching off of their membranes (microautophagy). 4. Secretory vesicles can degrade their secretory contents by fusing with the lysosomes.
    Virchows Archiv B Cell Pathology 02/1981; 36(2-3):219-34. DOI:10.1007/BF02912068
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    ABSTRACT: An electron microscopic, morphometric analysis of isolated rat hepatocytes revealed a 70% decrease in the early forms of autophagic vacuoles after administration of leucine. The lysosomal degradation of protein was reduced by only about 30% under the same conditions. These observations suggest that leucine is a major regulator of the bulk autophagy observable in the electron microscope, but that this type of autophagy contributes only about one-half of the total amount of protein degraded in lysosomes. Asparagine inhibited lysosomal protein degradation more strongly than did leucine, but had no significant effect on the amount of autophagic vacuoles. Leucine and asparagine would therefore seem to exert their effects on lysosomal protein degradation through different mechanisms.
    Experimental Cell Research 08/1981; 134(1):33-9. DOI:10.1016/0014-4827(81)90460-2 · 3.25 Impact Factor
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    ABSTRACT: Analogues and derivatives of six of the amino acids which most effectively inhibit protein degradation in isolated rat hepatocytes (leucine, asparagine, glutamine, histidine, phenylalanine and tryptophan) were investigated to see if they could antagonize or mimic the effect of the parent compound. No antagonists were found. Amino alcohols and amino acid amides tended to inhibit protein degradation strongly, apparently by direct lysosomotropic effect as indicated by their ability to cause lysosomal vacuolation. Amino acid alkyl esters and dipeptides inhibited degradation to approximately the same extent as did their parent amino acids, possibly by being converted to free amino acids intracellularly. Of several leucine analogues tested, four (L-norleucine, L-norvaline, D-norleucine and L-allo-isoleucine) were found to be as effective as leucine in inhibiting protein degradation. None of the analogues had any effect on protein synthesis. Since leucine appears to play a unique role as a regulator of bulk autophagy in hepatocytes, the availability of active leucine agonists may help to elucidate the biochemical mechanisms for control of this important process.
    Biochimica et Biophysica Acta 09/1981; 676(1):43-50. DOI:10.1016/0304-4165(81)90007-6 · 4.66 Impact Factor
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