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首页> 外文期刊>Phytochemistry >COMPARISON OF STRUCTURE AND KINETIC MECHANISM OF PHOSPHORYLASE FORMS ISOLATED FROM WATER YAM (DIOSCOREA ALATA) AND WHITE YAM (DIOSCOREA ROTUNDATA) TUBERS
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COMPARISON OF STRUCTURE AND KINETIC MECHANISM OF PHOSPHORYLASE FORMS ISOLATED FROM WATER YAM (DIOSCOREA ALATA) AND WHITE YAM (DIOSCOREA ROTUNDATA) TUBERS

机译：水山药和山药管分离的磷酸酶形式的结构和动力学机理的比较

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摘要

Two forms of phosphorylase from Dioscorea alata and one from D. rotundata were purified using various techniques of chromatography and electrophoresis. The molecular masses obtained for fractions I and II of D. alata phosphorylase were 120000 +/- 3000 and 170000 +/- 6800, respectively, while the molecular mass obtained for the phosphorylase from D. rotundata was 188000 +/- 10000. SDS gel electrophoresis indicated two subunit structures for fraction II and D. rotundata enzyme, while fraction I is a monomeric protein with a single polypeptide chain. Kinetic data are consistent with a degradative role of phosphorylase from white yam, while water yam tuber phosphorylase may play a synthetic role. Bisubstrate kinetics showed a double displacement mechanism in the direction of phosphorolysis for D. alata phosphorylase forms except fraction II, which indicated a single displacement mechanism only when P-i was varied at fixed starch concentrations. In the direction of glucan synthesis, a sequential mechanism was indicated for all the yam enzymes studied. However, D. rotundata phosphorylase differs from that of D. alata enzyme in that the latter showed a ping-pong mechanism only in the direction of starch degradation. Histidine has been identified as an amino acid residue that might be involved in catalysis.
机译：使用多种色谱和电泳技术纯化了薯Di的两种形式的磷酸化酶和罗汉果的一种。 D. alata磷酸化酶的级分I和II的分子量分别为120000 +/- 3000和170000 +/- 6800，而D. rotundata的磷酸化酶的分子量为188000 +/-10000。SDS凝胶电泳表明，第II部分和D. rotundata酶有两个亚基结构，而第I部分是具有一条多肽链的单体蛋白。动力学数据与白薯磷酸化酶的降解作用相一致，而水薯块茎磷酸化酶可能起合成作用。双底物动力学显示D.alata磷酸化酶形式的磷酸分解方向上的双重置换机制，除了部分II，这仅在P-i在固定的淀粉浓度下变化时才显示单一置换机制。在葡聚糖合成的方向上，表明了所研究的所有山药酶的顺序机制。然而，D。rotundata磷酸化酶与D. alata酶的不同之处在于后者仅在淀粉降解的方向上显示出乒乓机制。组氨酸已被鉴定为可能参与催化的氨基酸残基。

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