Reduction of ferric iron by L-lactate and DL-glycerol-3-phosphate in membrane preparations from Staphylococcus aureus and interactions with the nitrate reductase system

Abstract

Membrane fractions with L-lactate dehydrogenase, sn-glycerol-3-phosphate (G3P) dehydrogenase and nitrate reductase activities were prepared from S. aureus wild-type and hem mutant strains. These preparations reduced ferric to ferrous Fe with L-lactate or G3P as the source of reductant, using ferrozine to trap the ferrous Fe. Reduction of ferric Fe was insensitive to 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO) with L-lactate or G3P as reductant, but oxalate and dicumarol inhibited reduction with L-lactate as substrate. The membranes had L-lactate- and G3P-nitrate reductase activities, which were inhibited by azide and by HQNO. Reduction of ferric Fe under anaerobic conditions was inhibited by nitrate with preparations from the wild-type strain. This effect of nitrate was abolished by blocking electron transport to the nitrate reductase system with azide or HQNO. Nitrate did not inhibit reduction of ferric iron in heme-depleted membranes from the hem mutant unless hemin was added to restore L-lactate- and G3P-nitrate reductase activity. Reduced components of the electron transport chain that precede cytochrome b apparently serve as the source of reductant for ferric iron and these components may be oxidized preferentially by a functional nitrate reductase system.