Particulate Dihydroorotate Oxidase System From a Pseudomonad: Linkage With the Respiratory Chain

A particulate dihydroorotate oxidase system was prepared from a soil pseudomonad. Components of the respiratory chain participating in electron transport from dihydroorotate to molecular oxygen are bound non-heme iron, ubiquinone, cytochromes b and c, and cytochrome oxidase. Alternate pathways to oxygen are also operative. Inhibition by conventional respiratory inhibitors was incomplete. Dyes and added cytochrome c were readily reduced by dihydroorotate. Pyridine–adenine dinucleotide coenzymes were not reduced by the substrate. However, oxidase activities for these cofactors may have prevented any net reduction. The primary site of reaction with dihydroorotate probably consists of a dehydrogenase which is linked to the respiratory chain and is reactive with various dyes.In the absence of external electron acceptors or inhibitors, 0.5 mole of oxygen was consumed per mole of dihydroorotate oxidized. The anaerobic rate of reduction of bound cytochrome c, as studied by the stopped–flow technique, was slower than the maximum initial rates of orotate production.