Proteolytic digestion of Cl--ATPase in rat brain synaptosomes.

Abstract
Upon tryptic digestion of synaptosomes, ATPase activities decreased in the order of Cl--ATPase ?? Na+, K+-ATPase > anion-insensitive Mg2+-ATPase. Upon synaptosome treatment with hypotonic solution, C1--ATPase or anion-insensitive Mg2+-ATPase was slightly inactivated, while Na+, K+-ATPase underwent a much larger degree of inactivation. ATP-Mg inhibited the ATPase digestion in the hypotonic-solution-treated synaptosomes in a concentration-dependent manner, but not in the untreated synaptosomes. These results suggest that trypsin-digestible site of C1--ATPase are present on both sides of the synaptosomal plasma membrane, and the ATP-Mg binding site of the enzyme is located on the inner surface of the membrane.