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

Abstract

Hydrogen peroxide formation in light in isolated chloroplasts is markedly increased by the addition of potassium cyanide (KCN), diethyldithio-carbamate and 3-amino-l,2,4-triazol, whereas photophosphorylation is not affected by these compounds. Catalase activity of chloroplasts is inhibited by KCN, diethyl-dithiocarbamate and aminotriazol. Since furthermore the oxidation of chlorogenic acid requires light, we assume that the reduced cofactor in O2 catalyzed photophosphorylation is not reoxidized by phenoloxidase but by a chlorophyll sensitized photooxidation accompanied by hydrogen peroxide formation. In the absence of inhibitors the hydrogen peroxide is decomposed by catalase. Cyclic phosphorylation in the absence of O2 is not inhibited by dichlorophenyldimethylurea or o-phenan-throline. Photophosphorylation catalyzed by vitamin K or dichlorophenol-indophenol 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 phosphorylation without the participation of O2 ex-plains former results hitherto hard to fit into the known schemes of electron transport in chloroplasts.