The oxidation of manganese by illuminated chloroplast preparations

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Abstract
Chloroplast preparations oxidize Mn2+ in light but not, or to a much less extent, in darkness. In pyrophosphate the oxidation product accumulated as a soluble manganipyrophosphate. In phosphate an insoluble oxidation product was formed which, like MnO2, on treatment with pyrophosphate containing Mn2+ gave a soluble manganipyrophosphate. The oxidation products oxidize hydrazlne and were estimated manometrically by this reaction or spectrophotometrically as manganipyrophosphate. A sensitive spectrophotometric method of estimating manganipyrophosphate was described. The effect of variation of light intensity, period of illumination, concentration of chloroplast material and of Mn2+ was studied. Catalase partially inhibits the oxidation. Peroxidase increases the rate of oxidation. It is suggested that the oxidation is due, at least in part, to peroxidase systems and that a manganese oxidation-reduction cycle may play a part in the reactions of photosynthesis.