Two Functionally Different Dihydroorotic Dehydrogenases in Bacteria

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Abstract
We have investigated the relationship between the two kinds of dihydroorotic dehydrogenases produced by bacteria. A pseudomonad, capable of growth on a salts medium with glucose, aspartate, glycerol, or orotate as the carbon source, was isolated from lake bank mud. A particle-bound dihydroorotic dehydrogenase, similar to the biosynthetic enzyme in Escherichia coli, was formed by the pseudomonad when the carbon source was orotate, glucose, glycerol, or aspartate. A soluble, degradative nico-tinamide adenine dinucleotide phosphate-linked dihydrorotic dehydrogenase, as well as the particle-bound biosynthetic enzyme, was formed when the pseudomonad was cultivated on orotate. The biosynthesis enzyme links to oxygen or ferricyanide, but not to pyridine nucleotides. Zymobacterium oroticum, when cultivated on glucose, contained only the biosynthetic type of dihydrorotic dehydrogenase. The presence of two functionally different dihydroorotic dehydrogenases in the pseudomonad was suggested on the basis of the following observations: the two enzyme activities were separated by centrifugation; the pyridine nucleotide-linked activity was formed only when orotate was present in the growth medium; and the biosynthetic enzyme was stable to storage at [long dash]20 C for 4 months, whereas the degradative enzyme activity was destroyed by storage under these conditions.

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