Inhibitory effect of the partially resolved coordination isomers of chromic desferricoprogen on coprogen uptake in Neurospora crassa.

Two partially resolved chromatographic fractions of geometrical and optical isomers of the chromic complexes of desferricoprogen, a siderophore from Neurospora crassa, were obtained from high-pressure liquid chromatography on a reverse-phase matrix. The first fraction was identified as a cis complex with a 20% diastereomeric excess of the lambda isomer. The second fraction was identified as a mixture of several of the possible trans isomers with a net 20% diastereomeric excess of the delta isomers. These fractions were used to evaluate the stereospecificity of the coprogen-mediated iron uptake system with respect to the metal coordination center. Fraction II competitively inhibited coprogen uptake, whereas fraction I showed only slight inhibition. N. crassa accumulated chromium from fraction II faster than the rate of chromium uptake from fraction I. Neither fraction had a significant effect on the uptake of ferricrocin, suggesting that coprogen and ferricrocin are taken up by different receptor systems.