Native and Latent Forms of Liver Phosphorylase Phosphatase

Abstract

The directly measurable (native) phosphorylase phosphatase [EC 3.1.3.7] present in a fresh mouse liver extract is bound to particulate glycogen and is not inhibited by heat-stable inhibitors. Treatment of the extract with trypsin [EC-3.4.21.4] or ethanol at room temperature caused a more than 10-fold increase in phosphorylase phosphatase activity. This increased activity stems from the activation of completely inactive (latent) enzyme, the major part of which is present in the high-speed supernatant. The trypsin-revealed activity can be completely blocked by heat-stable inhibitors. Treatment of the animal with glucocorticoids increases, and fasting decreases the activity of the native phosphorylase phosphatase. The level of latent enzyme, however, is unaffected by these treatments. The major portion of synthase phosphatase [EC 3.1.3.42] in the fresh liver extract is bound to glycogen. This enzyme is inhibited by the heat-stable inhibitor-2 and inactivated by trypsin or ethanol and by several treatments that have little effect on phosphorylase phosphatase. Upon DEAE-cellulose chromatography at 0.degree. C of a liver extract, phosphorylase phosphatase and synthase phosphatase were resolved as separate, single peaks. If the preparation was not kept at 0.degree. C during the entire procedure, 2 peaks of each enzyme were observed. Under these conditions the first peak of phosphorylase phosphatase and of synthase phosphatase coincided. Apparently synthase phosphatase and phosphorylase phosphatase, in their native form, are distinct enzymes.