Studies on plasma membranes: XI. Inorganic pyrophosphatase, PP1-glucose phosphotransferase and glucose-6-phosphatase in plasma membranes and microsomes isolated from rat and mouse livers and hepatomas

Abstract 1. 1. Plasma membranes and microsomes were isolated from rat and mouse livers and hepatomas, and the specific activities of the membrane-bound enzymes inorganic pyrophosphatase (EC 3.6.1.1), PP 1 -glucose phosphotransferase and glucose-6-phosphatase (EC 3.1.3.9) were determined. 2. 2. The effect of deoxycholate, NH 4 OH pretreatment, lipid peroxidation, partial lipid extraction, membrane concentration and pH changes on the enzyme activities were studied. Under these conditions plasma-membrane and microsomal pyrophosphatase activities behaved differently. Also with respect to the two other enzyme activities, a number of differences in reaction have been noted. 3. 3. The distribution of enzyme activities over smooth and rough microsomal membrane fractions differed for rat liver and rat hepatoma. 4. 4. It is concluded that plasma membranes contain at least an authentic inorganic pyrophosphatase (active at acid pH) distinct from the microsomal enzyme.