Biosynthesis of the XXXX - @entity5334 cofactor and the @entity5334 cofactor in @entity3274 : effect of @entity599 source.

@entity1568 @entity68 @entity526 @entity1507 @entity3274 @entity1434 @entity7051 @entity599 @entity5334 @entity597
NifQ- and Mol- mutants of @entity3274 show an elevated @entity5334 requirement for @entity1568 fixation. Substitution of @entity1434 for @entity597 as the @entity599 source in the medium reduced the @entity5334 requirement of these mutants to levels required by the wild type. @entity1434 also increased the intracellular @entity5334 accumulation of NifQ- and Mol- mutants. @entity1434 did not affect the @entity5334 requirement or accumulation in wild-type @entity3274 . @entity597 transport and metabolism in @entity3274 were repressed by @entity1434 . However, the effect of @entity1434 on the @entity5334 requirement could not be explained by an interaction between @entity597 and molybdate at the transport level. @entity1434 increased the @entity5334 requirement of Mol- mutants for @entity1507 reductase activity by at least 100-fold. @entity1434 had the same effect on the @entity5334 requirement for @entity1507 reductase activity in @entity526 ChlD- mutants. This shows that @entity1434 does not have a generalized effect on @entity5334 metabolism. Millimolar concentrations of @entity7051 inhibited nitrogenase and @entity1507 reductase derepression with @entity597 as the @entity599 source, but not with @entity1434 . The inhibition was the result of a specific antagonism of @entity597 metabolism by molybdate. The effects of nifQ and mol mutations on nitrogenase could be suppressed either by the addition of @entity1434 or by high concentrations of molybdate. This suggests that a @entity599 donor and @entity5334 interact at an early step in the biosynthesis of the @entity68 - @entity5334 cofactor. This interaction might occur nonenzymatically when the levels of the reactants are high.
