A protein from leaves catalysing the reduction of metmyoglobin and triphosphopyridine nucleotide by illuminated chloroplasts

Abstract

A purified protein fraction from leaves, previously shown to be active in catalyzing the reduction of some haem-protein compounds by illuminated chloroplasts (Davenport and Hill, 1960), will also catalyze the reduction of triphosphopyridine nucleotide (TPN) but not diphosphopyridine nucleotide. Under appropriate conditions the rate of reduction of TPN but not that of metmyoglobin is stimulated up to threefold by including adenosine diphosphate, orthophosphate and magnesium ions in the reaction mixture. Arsenate will replace phosphate in producing this stimulation. The reduction of metmyoglobin is progressively inhibited by TPN alone and by TPN with the phosphate-acceptor system present. The protein obtained by Davenport and Hill (1960) has the properties of a more highly purified form of the photosynthetic pyridine nucleotide reductase of San Pietro and Lang (1958). It was found that the latter preparation is active in catalyzing the reduction of metmyoglobin and could be further purified by electrophoresis on paper to give a product indistinguishable from that obtained by Davenport and Hill (1960).