Evidence that calmodulin is in the chloroplast of peas and serves a regulatory role in photosynthesis.

phenothiazine drugs in a Ca2+-dependent manner, is inhibited by phenothiazine drugs, is heat stable, and has other molecular properties similar to calmodulin. To test the hypothesis that the Ca”-calmodulin-activated NAD kinase catalyzes the light-induced conversion of NAD to NADP in chloroplasts, calmodulin-binding drugs were used. These drugs inhibited the lightinduced NAD to NADP conversion at concentrations near those required to inhibit calmodulin, and these results were thus consistent with the hypothesis. These same drugs inhibit photosynthetic oxygen evolution while chlorpromazine sulfoxide, which is ineffective toward calmodulin, does not. These results were consistent with a role for calmodulin in the regulation of NAD kinase and photosynthesis.