A MODEL SYSTEM FOR NAD(P)H-DEPENDENT REDUCTION OF MANGANESE-DIOXIDE MEDIATED BY FERROUS CHELATE IN WHITE-ROT FUNGUS, PHANEROCHAETE SORDIDA YK-624

Manganese dioxide was reduced to Mn(II) in a liquid culture of Phanera chaete sordida YK-624 which showed a high bleaching ability of unbleac hed hardwood kraft pulp. The reduction of manganese dioxide by the was hed mycelia was dependent on both Fe(II) and a metal chelator. The man ganese dioxide-reducing activity of the washed mycelia was proportiona l to the concentrations of ferrous chelate and NADH. Ferrous chelate r educed manganese dioxide to Mn(II) while being oxidized to ferric chel ate, and the cell-free extract from P. sordida YK-624 catalyzed the re duction of ferric chelate with NAD(P)H. These results suggest that fer rous chelate reduces manganese dioxide, and that the produced ferric c helate was reduced by NAD(P)H-dependent reductase in P. sordida YK-624 to regenerate ferrous chelate. An Fe(II)-reducing system may play a r ole in the reduction of Fe(III) to Fe(II), which is used for reducing manganese dioxide to Mn(II).