Abstract
When the crude phosphoprotein phosphatase fraction of rat liver cytosol was treated with 80% aqueous ethanol at room temperature, the activity with phosphorylase a as substrate was increased by 110%, but those with glycogen synthase D and phosphohistone were decreased by 53 and 34%, respectively. Chromatography of the ethanol-treated fraction on DE-52 revealed that while phosphoprotein phosphatase IA (Mr=69, 000) remained to exist even though it was reduced, phosphatases IB (Mr=300, 000) and II (Mr=160, 000) were totally replaced by a new phosphatase form with an approximate molecular weight of 35, 000. This low molecular weight form has been designated phosphatase III. When partially purified phosphatases IB and II were separately treated with ethanol, they were converted to phosphatase III. These results suggest that phosphoprotein phosphatases IB and II, but not IA, contain phosphatase III as a subunit. Phosphatases IB and II, however, must differ in structure since “IB to III” is accompanied by an increase in phosphorylase phosphatase activity much greater than that for “II to III”
