Yokota A, Kawabata A, Kitaoka S
Department of Agricultural Chemistry, University of Osaka Prefecture, Sakai, Osaka 591.
Plant Physiol. 1983 Apr;71(4):772-6. doi: 10.1104/pp.71.4.772.
The mechanism for decarboxylating the carboxyl carbon of glycolate was studied in Euglena gracilis Z, which liberates more than 70% of the carboxyl carbon as CO(2) during glycolate metabolism.In the isolated mitochondria of E. gracilis, glycolate was oxidized to glyoxylate, 25% of which was aminated to glycine, with the remaining unchanged in the presence of glutamate; in the absence of the amino donor, glyoxylate was not changed. Irrespective of the presence or absence of the amino donor, no decarboxylation took place in Euglena mitochondria. In Euglena chloroplasts glyoxylate was actively decarboxylated by the action of hydrogen peroxide generated by the reaction of a Mn(2+)-dependent NADPH oxidase. This enzyme was purified 120-fold over the crude extract and some of its properties studied. Oxidation of one molecule of NADPH was accompanied by the formation of one molecule of H(2)O(2); the NADPH oxidation was not attributable to the action of l-ascorbate peroxidase, the sole peroxidase present in E. gracilis. Specific participation of chloroplasts and mitochondria in glycolate metabolism is discussed.
对纤细裸藻Z中乙醇酸羧基碳脱羧的机制进行了研究，在乙醇酸代谢过程中，该藻将超过70%的羧基碳以CO₂的形式释放出来。在分离出的纤细裸藻线粒体中，乙醇酸被氧化为乙醛酸，其中25%被胺化为甘氨酸，其余部分在有谷氨酸存在的情况下保持不变；在没有氨基供体的情况下，乙醛酸没有变化。无论有无氨基供体，裸藻线粒体中均未发生脱羧反应。在裸藻叶绿体中，乙醛酸在锰离子依赖的NADPH氧化酶反应产生的过氧化氢作用下被积极地脱羧。该酶比粗提物纯化了120倍，并对其一些性质进行了研究。一分子NADPH的氧化伴随着一分子H₂O₂的形成；NADPH的氧化不归因于纤细裸藻中唯一存在的过氧化物酶——L-抗坏血酸过氧化物酶的作用。讨论了叶绿体和线粒体在乙醇酸代谢中的具体参与情况。
