Electron transport dependent adenosine triphosphatase activity in castor bean endosperm mitochondria

The release of inorganic phosphate from ATP by mitochondriaisolated from endosperms of castor bean (Ricinus communis) wasstimulated by Mg⁺⁺, but not by Ca⁺⁺. EDTA, succinate, NADH₂or oligomycin depressed the reaction. The depression by succinatewas removed by KCN, antimycin A or anoxia. DNP alone did notaffect activity but did stimulate the Pi release in the presenceof succinate under aerobic conditions. Enhanced Pi release inthe presence of succinate and DNP was cancelled by KCN, antimycinA, oligomycin or anoxia. On the basis of these results, themechanism of ATPase action in castor bean endosperm mitochondriais discussed. (Received January 27, 1969; )