Enzymes of plasma membranes of liver.

The aim of the work was to provide tentative criteria for distinguishing between authentic and contaminating activities of plasma membrane preparations from rat liver. To this end, the specific activities and extractabilities were studied of eight activities found in the membrane preparations and in liver microsomes. Liver microsomes were examined since contaminants of the plasma membrane preparations, when they could be detected, were invariably derived from rough endoplasmic reticulum. One of the activities of the plasma membrane preparations (a threonine-dependent adenosine triphosphate-inorganic pyrophosphate exchange activity) appeared to be a soluble adsorbed contaminant; three others (an esterase, P-glucuronidase, and an amylase) seemed to derive from contamination with rough endoplasmic reticulum; and the remaining four activities (acid and alkaline phosphatase (substrate, p-nitrophenyl phosphate), a diphosphopyridine nucleotide-splitting activity, and phosphodiesterase) were considered to be components of the plasma membrane.