Inhibition by Cyanide of the Photochemical Activity of Isolated Chloroplasts

Abstract

CYANIDE is an effective inhibitor of the photosynthesis of most plants. Photosynthesis in weak light is relatively insensitive to cyanide, whereas studies with flashing light show that cyanide does not affect the yield of oxygen from each light flash if the dark time between flashes is made long enough. Experiments of this type, together with other lines of evidence, all indicate that the cyanide-sensitive phase of photosynthesis is the primary reaction in the fixation of carbon dioxide¹. It should not be concluded, however, that all the other reactions in photosynthesis are insensitive to cyanide. The apparent lack of sensitivity of other reactions may result simply from a low concentration of the carboxylating enzyme system relative to other enzymes. Under such conditions, cyanide would appear to be selective for the carbon dioxide fixation process¹.