Light-Dependent Oxygen Metabolism of Chloroplast Preparations. II. Stimulation by Manganous Ions

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Abstract
A mass spectrometer was used to measure simultaneously the rates of consumption and production of O2 in unstimulated and Mn-stimulated light-dependent reactions of chloroplasts prepared from Phytolacca americana. Both rates were stimulated on addition of manganous ions to Mehler reaction mixtures and similar stimulations of the related exchange reaction were observed. These experiments indicated that the action of Mn is the result of a reaction with the oxidized product of photoylsis. A reaction mechanism has been postulated whereby Mn mediates peroxide formation from the (OH)-product of the splitting of water. This provides an alternate pathway which results in more efficient removal of this product and accounts for the stimulation of net O2 uptake by manganous ions.