Taylor W H, Taylor C D, Taylor M L
J Bacteriol. 1974 Jul;119(1):98-105. doi: 10.1128/jb.119.1.98-105.1974.
Some of the catalytic properties of the biosynthetic dihydroorotate dehydrogenase purified from an anaerobic bacterium, Lactobacillus bulgaricus, are described. Studies with p-hydroxymercuribenzoate, N-ethylmaleimide, and mercuric chloride showed that sulfhydryl groups are necessary for transfer of electrons from dihydroorotate to a variety of electron acceptors. Protection studies with substrates for the enzyme indicated that free sulfhydryl groups at or near the active center are required for catalytic activity. Evidence is presented for the production of superoxide free radicals during reaction of the enzyme with molecular oxygen. Inhibitor studies with Tiron indicated that reduction of cytochrome c by the enzyme may involve the superoxide free radical as an intermediate. Orotate, one of the substrates for the enzyme, has been found to be a competitive inhibitor for the dihydroorotate site. The K(i) for orotate as estimated by several techniques is 0.1 mM. The K(m) for dihydroorotate with ferricyanide as the electron acceptor is estimated to be 0.5 mM.
本文描述了从厌氧细菌保加利亚乳杆菌中纯化得到的生物合成二氢乳清酸脱氢酶的一些催化特性。对对羟基汞苯甲酸、N-乙基马来酰亚胺和氯化汞的研究表明，巯基对于电子从二氢乳清酸转移到多种电子受体是必需的。对该酶底物的保护研究表明，活性中心或其附近的游离巯基是催化活性所必需的。有证据表明该酶与分子氧反应过程中会产生超氧自由基。用钛铁试剂进行的抑制剂研究表明，该酶还原细胞色素c可能涉及超氧自由基作为中间体。乳清酸是该酶的底物之一，已被发现是二氢乳清酸位点的竞争性抑制剂。通过几种技术估算，乳清酸的K(i)为0.1 mM。以铁氰化物作为电子受体时，二氢乳清酸的K(m)估计为0.5 mM。
