INVIVO PROGESTERONE REGULATION OF PROTEIN PHOSPHATASE-ACTIVITY IN XENOPUS OOCYTES

Exogenous β casein, previously phosphorylated in vitro by protein kinase A and casein kinase II, was microinjected into Xenopus oocytes to monitor in vivo protein phosphatase activities. Phosphatase activities were 1.6 and 3.4 fmol/min/oocyte, respectively, for β casein phosphorylated by casein kinase II and β casein phosphorylated by protein kinase A. Progesterone induced an early decrease (35% after 10 min) in phosphatase activity restricted to the protein kinase A sites of β casein. © 1990.