[Show abstract][Hide abstract] ABSTRACT: Vicianin hydrolase, which catalyzes the hydrolysis of vicianin (K(m), 4.9 millimolar) to (R)-mandelonitrile and vicianose at an optimum pH of 5.5, was extensively purified from the young fronds and fiddleheads of the squirrel's foot fern (Davallia trichomanoides Blume) using DEAE-cellulose and Ultrogel HA chromatography. The native molecular weight of the enzyme was 340,000, and the isoelectric point was 4.6 to 4.7. SDS-PAGE analysis yielded three polypeptides with molecular weights of 56,000, 49,000, and 32,500. The enzyme hydrolyzed only a narrow range of glycosides and, among cyanogenic glycosides, exhibited a strict requirement for (R)-epimers and a preference for disaccharides over monosaccharides. (R)-Amygdalin, (R)-prunasin and p-nitrophenyl-beta-d-glucoside were hydrolyzed at 27, 14, and 3%, respectively, of the rate of vicianin hydrolysis. Mixed substrate studies showed that (R)-vicianin, (R)-prunasin, and p-nitrophenyl-beta-d-glucoside competed for the same active site. The enzyme was significantly inhibited by castanospermine, delta-gluconolactone, and p-chloromercuriphenylsulfonate. Failure to recognize concanavalin A-Sepharose 4B and to stain with periodic acid-Schiff reagent indicated that the enzyme was not a glycoprotein.
[Show abstract][Hide abstract] ABSTRACT: Enzymatic syntheses of water-soluble alpha-tocopheryl glycosides were carried out in di-isopropyl ether using amyloglucosidase from Rhizopus mold or beta-glucosidase isolated from sweet almond. Optimum conditions for the amyloglucosidase were: alpha-tocopherol 0.5 mmol, D-glucose 0.5 mmol, 400 activity unit (AU) amyloglucosidase, 0.2 mM pH 7 phosphate buffer and 72 h; and for the beta-glucosidase: alpha-tocopherol 0.5 mmol, D: -glucose 0.5 mmol, 110 AU beta-glucosidase, 0.1 mM pH 6 phosphate buffer and 72 h. Out of 11 carbohydrates employed, amyloglucosidase reacted only with D-glucose to give 50% of 6-O-(alpha-D-glucopyranosyl)alpha-tocopherol. However, the beta-glucosidase gave 6-O-(beta-D-glucopyranosyl)alpha-tocopherol, 6-O-(alpha-D-galactopyranosyl)alpha-tocopherol, 6-O-(beta-D-galactopyranosyl)alpha-tocopherol, 6-O-(alpha-D-mannopyranosyl)alpha-tocopherol and 6-O-(beta-D-mannopyranosyl)alpha-tocopherol in yields ranging from 10-25%. Water solubility of 6-O-(alpha-D-glucopyranosyl)alpha-tocopherol was 26 g/l at 25 degrees C. alpha-Tocopheryl glycosides showed antioxidant activities with IC(50) values from 0.5 to 1 mM and angiotensin-converting enzyme (ACE) inhibitory activity with IC(50) values from 1.3 to 2.6 mM.
[Show abstract][Hide abstract] ABSTRACT: Salicortin, a natural product abundant in most members of the Salicaceae family, is a mechanism-based inactivator of Agrobacterium faecalis beta-glucosidase. Inactivation is delayed in the presence of competitive inhibitors, thereby demonstrating the requirement for an enzyme-bound salicortin before inactivation. Product studies suggest that inactivation proceeds via a quinone methide intermediate formed by the fragmentation of the aglycone of salicortin while it is bound to the enzyme. Tryptic digest and HPLC/MS studies confirm the role of quinone methide attack and also show that the enzyme undergoes multiple modifications. In addition, when the inactivation was run in the presence of a mutant inactive form of the enzyme, HPLC/MS analyses clearly showed no modification of the mutant enzyme, demonstrating that the quinone methide does not exist in free solution and suggesting that inactivation is active-site directed.
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