Catabolism of Cyanogenic Glycosides by Purified Vicianin Hydrolase from Squirrel's Foot Fern (<i>Davallia Trichomanoides</i> Blume)
作者:Pauline A. Lizotte、Jonathan E. Poulton
DOI:10.1104/pp.86.2.322
日期:1988.2.1
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-β-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-β-d-glucoside competed for the same active site. The enzyme was significantly inhibited by castanospermine, δ-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.
利用 DEAE-纤维素和 Ultrogel HA 色谱法,从松鼠脚蕨类植物(Davallia trichomanoides Blume)的嫩叶和蕨头上广泛纯化了藤黄素水解酶,该酶催化藤黄素(K m,4.9 毫摩尔)在最佳 pH 值为 5.5 时水解为(R)-扁桃腈和藤黄素。该酶的原生分子量为 340,000,等电点为 4.6 至 4.7。SDS-PAGE 分析得出了三种多肽,分子量分别为 56,000、49,000 和 32,500。该酶只水解范围较窄的苷类,在氰苷类化合物中,它对 (R)-epimers 有严格的要求,对双糖的偏好高于单糖。(R)-苦杏仁苷、(R)-樱桃苷和对硝基苯基-β-d-葡萄糖苷的水解速度分别为葡萄苷水解速度的 27%、14% 和 3%。混合底物研究表明,(R)-藤黄素、(R)-樱黄素和对硝基苯基-β-d-葡萄糖苷竞争同一个活性位点。蓖麻毒素、δ-葡萄糖酸内酯和对氯巯基苯磺酸盐对该酶有明显的抑制作用。该酶不能识别 concanavalin A-Sepharose 4B,也不能用周期性酸-Schiff 试剂染色,这表明该酶不是糖蛋白。