Untersuchungen über die Beteiligung des Sauerstoffs in photosynthetischen Reaktionen mit Hilfe von Hemmstoffen

Abstract

Hydrogenperoxide formation in the light in isolated chloroplasts is markedly increased upon the addition of KCN, diethyldithiocarbamate and 3-amino-1.2.4-triazol, whereas photophosphorylation is not influenced by these compounds. Catalase activity of chloroplasts is inhibited by KCN, diethyldithiocarbamate and aminotriazol. Since furthermore the oxidation of chlorogenic acid requires light, we assume that the reduced cofactor in oxygen catalyzed photophosphorylation is not reoxidized by phenoloxidase but by a chlorophyll sensitized photoöxidation accompanied by H2O2-formation. In the absence of inhibitors the H2O2 is decomposed by catalase. The influence of dichlorphenyldimethylurea and o-phenanthroline on cyclic photophosphorylation in the absence of oxygen has been investigated. Photophosphorylation catalyzed by Vitamin K or dichlorphenolindophenol is not inhibited provided that the cofactor is in the reduced state at the beginning of the reaction. The finding that indophenols are catalysts of cyclic photophosphorylation without the participation of oxygen explains former results hitherto hard to fit into the known schemes of electrontransport in chloroplasts.