Enzymatic Iron Oxidation and Reduction in magnetite Synthesizing Magnetospirillum Magnetotacticum

摘要

We investigated the enzymatic reduction and oxidation of iron in M.inagnctaracticum which synthesizes magnetite at room temperature. NADH-Fe(IlI) reductase with the molecular mass of 36kDa was purified from the bacterium. The enzyme was located in cytoplasm and utilized NADH and NADPH in the presence of FMN as rcductant and showed maximum activity at pH 7.0. The Km for NADH and NADPH were about 4.3/(M and 1 9/iM, respectively. The enzymatic activity was strongly inhibited by Zn2+. On the other hand, the dissimilatory nitrite reductase of M.magnetotacticum showed high Fe(H)-nitrite oxidoreductase activity. The enzyme was located in periplasmic space and could be isolated from the magnetite-containing cells but not from the non-magnetic cells. The enzyme composed of two identical subunits with a molecular mass of 54 kDa, each containing a c - and -lype henie. The activity was about 0.57 mol ferrous iron/mol of enzyme/sec at pH 8.0. The oxidized ferrous iron/reduced nitrite ratio was about 1.4, indicating that nitrite was reduced to NO. Furthermore, M.magnetotacticum synthesized much more magnetites when Ihe bacterium grew using denitrification, the dissimilatory reduction of nitrate to dinitrogen via nitrite, nitric oxide and nitrous oxide. These results propose that the dissimilalory nitrite reductase of M.magnetotacticum may participate as Fc(II) oxidizing enzyme in magnetite synthesis under microaerobic conditions.