In vivo actions of protein phosphatase inhibitor-2 in Xenopus oocytes.

Meiotic maturation of amphibian oocytes induced by progesterone is known to be regulated by protein phosphorylation. To investigate a possible role for protein phosphatase-1 in this process, the effect of phosphatase inhibitor-2 was determined on the in vivo rate of dephosphorylation of phosphorylase a and on the rate of oocyte maturation. Dephosphorylation of microinjected phosphorylase a was inhibited up to 40% in the presence of inhibitor-2, with half-maximal inhibition at an intracellular concentration of 0.6 microM. Inhibitor-2 also caused over a 3-fold increase in the half-time for maturation, suggesting a possible role for protein phosphatase-1 in the regulation of meiosis.