Effects of inhibitors of catalase on photosynthesis and on catalase activity in unwashed preparations of intact chloroplasts.

The catalase activity of unwashed preparations containing intact spinach (Spinacia oleracea L.) chloroplasts is inhibited both by cyanide and by azide at concentrations which also cause inhibition of photosynthetic CO(2)- dependent O(2) evolution.Aminotriazole can also be used to inhibit this contaminant catalase, and in this case inhibition of catalase can be achieved at aminotriazole concentrations which have little effect on the rate of photosynthetic CO(2) fixation. Aminotriazole may be used as a specific inhibitor of catalase in order to demonstrate inhibition of photosynthesis by added H(2)O(2).It is therefore concluded that inhibition of photosynthesis by cyanide and azide does not necessarily result from inhibition of catalase in the chloroplast preparation, and that intact chloroplasts do not produce inhibitory concentrations of H(2)O(2) under the best experimental conditions for CO(2) fixation.