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. 1974 Jul;119(1):98–105. doi: 10.1128/jb.119.1.98-105.1974

Biosynthetic Dihydroorotate Dehydrogenase from Lactobacillus bulgaricus: Partial Characterization of the Enzyme

W Herman Taylor 1, Craig D Taylor 1, Mary L Taylor 1
PMCID: PMC245578  PMID: 4366023

Abstract

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 Ki for orotate as estimated by several techniques is 0.1 mM. The Km for dihydroorotate with ferricyanide as the electron acceptor is estimated to be 0.5 mM.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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