A novel ferric reductase purified from Magnetospirillum gryphiswaldense MSR-1

A ferric reductase was purified into an electrophoretically homologous state from Magnetospirillum gryphiswaldense MSR-1 strain. The enzyme was found within the cytoplasm and associated with the cytoplasmic membrane. The molecular weight of the purified enzyme was calculated as 16.1 kDa using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and was almost identical to that calibrated using agarose gel filtration chromatography. It was NADH-dependent and required flavin mononucleotide as a cofactor. The optimal reaction temperature and pH values were 30 degrees C and 6.5, respectively. The K(m) and Vmax values for ferric citrate were 45.1 microM: and 1.216 microM: min(-1), respectively. Though ferric reductase activity could be inhibited by Co(2+), Cu(2+), Mn(2+), and Zn(2+), even high concentrations of Mg(2+) ions have failed to accomplish such enzyme inhibition. Furthermore, the molecular weight, the N-terminal sequence, and the activity of ferric reductase from MSR-1 are not matching with the enzyme preparation obtained from an analogous strain M. magnetotacticum (MS-1). Therefore, it is concluded that the ferric reductase of M. grysphiwaldense and M. magnetotacticum strains are two different enzymes.