Abstract
Phosphoprotein phosphatases [EC 31. 3. 16] acting on P-H 2 B histone, P-H 1 histone, phosphorylase α [EC 2. 4. 1. 1] and glycogen synthase b [EC 2. 4. 1. 11] were surveyed in cytosols from various rat tissues and erythrocytes by gel-filtration on Sephadex G-200. A main phosphoprotein phosphatase (Mr=200, 000) in tissue cytosols showed preference for phosphorylated histones. In contrast to tissue cytosols, erythrocyte cytosol contained a major phosphoprotein phosphatase (Mr=100, 000) which showed strong preference for phosphorylase α and synthase b. Other phosphoprotein phosphatases which preferred phosphorylase α were detected in cytosols from liver, kidney, spleen, and adipose tissue. The molecular weights of the phosphatases were estimated to be 140, 000 for liver enzyme and about 90, 000 for kidney, spleen, and adipose tissue enzymes. A phosphoprotein phosphatase (Mr=54, 000) which preferred synthase b and P-H 2 B histone was also found in cytosols from various tissues and erythrocytes. This phosphatase was most abundant in liver cytosol and showed strong dependency on Mg2+ and Mn2+. This enzyme was different from other phosphoprotein phosphatases in specificities for different phosphorylated sites on glycogen synthase b. Although treatment with 80% ethanol did not affect the size of liver 54, 000 molecular weight enzyme, the same treatment lowered the molecular weights of the major erythrocyte enzyme (Mr=100, 000), the main skeletal muscle, liver, and kidney enzymes (Mr=200, 000), liver 140, 000 molecular weight enzyme and kidney 93, 000 molecular weight enzyme to about 30, 000. As a result of this conversion, P-H 1 histone phosphatase activities and Mg2+ requirements for P-H 2 B histone phosphatase activities of these enzymes were greatly suppressed. Phosphorylase phosphatase activities of the 200, 000 and 140, 000 molecular weight enzymes were significantly enhanced, but the activity of the 100, 000 molecular weight enzyme was essentially unchanged and that of the 93, 000 molecular weight enzyme was slightly suppressed. Synthase phosphatase activities of the 200, 000 molecular weight enzymes increased 2-3-fold, but the activities of the other enzymes were either unaffected or insignificantly suppressed. The 30, 000 molecular weight enzymes derived from these enzymes showed same physical and catalytic properties, suggesting that the multiple molecular forms of phosphoprotein phosphatases (except for the 54, 000 molecular weight enzyme) contained a common 30, 000 molecul_??_r weight catalytic subunit(s).
