A novel ATPase in the chromaffin granule membrane

The ATPase activity of the chromaffin granule membrane was found to differ profoundly from that of the mitochondrial inner membrane. First, mitochondrial ATPase is much more sensitive to low concentrations of dicyclohexylcarbodiimide than the chromaffin granule ATPase. Second, analysis of chromaffin granule preparations by immune replication revealed that mitochondrial contamination (as measured with an antibody against cytochrome c oxidase) could account for the presence of mitochondrial-type ATPase. Third, exposure of chromaffin granule preparation to sodium bromide removed the mitochondrial-type ATPase, but left over 70% of the total ATPase activity of the chromaffin granules intact. Finally, after solubilization of the chromaffin granule membranes with detergents, a novel ATPase could be separated from the mitochondrial-type ATPase. It is proposed that this novel ATPase represents most of the ATPase activity of the chromaffin granules and that the mitochondrial-type ATPase reflects contamination by mitochondria.