Ldenosine-Triphosphatase Actifities of Erythrocyte Stroma and the Substrate Permeability

Abstract

Effects of conditions of preparing and storing human erythrocyte stroma on ATPase activities of the stroma, determined in the presence of added substrate and cofactors, were investigated.
After the first hypotonic treatment of erythrocytes, the obtained stroma showed rather low activities of both Mg-ATPase and Na-K-sensitive ATPase, which were increased markedly after homogenization of the stroma. The stroma obtained after repeated hypotonic treatments exhibited a maximal level of enzymicac tivities which did notchange after homogenization. Such stroma preparation, however, began to reduce ATPase activities after being kept overnightin an isotonic medium. These results indicate that the measured activities of these ATPases are dependent upon the degree of permeability of the stroma to the substrate or cofactors externally added to the reaction mixture.