The role of ferrichrome reductase in iron metabolism of Ustilago sphaerogena.

Ferrichrome, the ferric ionophore for Ustilago sphaerogena, can serve as a source of iron for the enzyme ferrochelatase (protoheme ferrolyase, EC 4.99.1.1) in this organism, but only after enzymatic removal of the iron from its carrier. U. sphaerogena contains a specific ferrichrome reductase (NADH:ferrichrome oxidoreductase) which catalyzes cellular dissociation of the complex by reduction of the metal to the ferrous state. A spectrophotometric assay was developed based on trapping of the ferrous ion produced by ferrozine. There is an apparent inhibition by oxygen which is thought to be due to re-oxidation of the metal under the assay conditions. The close structural analogue, ferrichrome A, is not a substrate, nor is the ester type siderochrome ferric hexahydro-N,N',N"-triacetylfusarinine C. Aluminum desferriferrichrome is inhibitory. The importance of this enzyme for the metabolism of iron in this organism is discussed.