Wolcott J H, Ross C
Plant Physiol. 1967 Feb;42(2):275-9. doi: 10.1104/pp.42.2.275.
This report includes results demonstrating the existence of orotidine-5'-phosphate decarboxylase and orotidine-5'-phosphate pyrophosphorylase in plant leaves. The decarboxylase enzyme, purified 8 fold from leaves of etiolated pinto beans (Phaseolus vulgaris L.), had a pH optimum of 6.3. It was strongly inhibited by 6-azauridine-5'-phosphate; a concentration of 12 mum decreased the reaction rate 60%. The enzyme was not dependent upon magnesium ions or inhibited by p-chloromercuribenzoate. It was present in other parts of the bean plant and was found in young leaves of tomato (Lycopersicon esculentum Mill.) and Canada thistle (Cirsium arvense L.)The enzyme orotidine-5'-phosphate pyrophosphorylase, which catalyzes the formation of orotidine-5'-phosphate from orotic acid and 5-phosphoribosyl-1-pyrophosphate, was found in the etiolated bean leaves, and was also present in the leaves of tomato and Canada thistle. It was stimulated by manganous or magnesium ions and had a pH optimum of 7.2. The K(m) value obtained by varying the concentrations of 5-phosphoribosyl-1-pyrophosphate was 75 mum, and when orotic acid was varied the resulting K(m) was 3.5 mum. The presence of these 2 enzymes in higher plants, combined with previous results with inhibitors and labeled metabolites, indicates that the normal pathway of pyrimidine nucleotide synthesis in higher plants proceeds through orotic acid and OMP.
本报告包含的结果表明，植物叶片中存在乳清苷-5'-磷酸脱羧酶和乳清苷-5'-磷酸焦磷酸化酶。从黄化菜豆（菜豆属普通菜豆）叶片中纯化8倍的脱羧酶，其最适pH值为6.3。它受到6-氮杂尿苷-5'-磷酸的强烈抑制；12 μmol的浓度使反应速率降低60%。该酶不依赖镁离子，也不受对氯汞苯甲酸的抑制。它存在于菜豆植株的其他部位，也存在于番茄（番茄属番茄）和加拿大蓟（蓟属田蓟）的幼叶中。催化从乳清酸和5-磷酸核糖-1-焦磷酸形成乳清苷-5'-磷酸的乳清苷-5'-磷酸焦磷酸化酶，在黄化菜豆叶片中被发现，也存在于番茄和加拿大蓟的叶片中。它受到锰离子或镁离子的刺激，最适pH值为7.2。通过改变5-磷酸核糖-1-焦磷酸的浓度获得的K(m)值为75 μmol，当改变乳清酸浓度时，得到的K(m)为3.5 μmol。高等植物中这两种酶的存在，结合先前使用抑制剂和标记代谢物的结果，表明高等植物中嘧啶核苷酸合成的正常途径是通过乳清酸和乳清苷一磷酸进行的。
