Nucleoside Triphosphate Pyrophosphohydrolase of the Plasma Membrane of the Liver Cell

An activity, named nucleoside triphosphate pyrophosphohydrolase, has been found in plasma membrane preparations from rat liver. The enzyme catalyzes the formation of inorganic pyrophosphate from adenosine triphosphate (but not from adenosine diphosphate) and other nucleoside triphosphates by a reaction that appears to be a simple hydrolysis. Evidence is presented to show that the activity is an authentic component of the membranes and that it is largely or completely absent from the liver microsome fraction.