Involvement of a calcium‐phospholipid‐dependent protein kinase in the maturation of Xenopus laevis oocytes

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Abstract
It has been described that phosphorylation, and dephosphorylation, of specific proteins is associated with key events of the cell cycle and is likely to be due to activation of kinase(s). From our results, the presence of calcium-phospholipid-dependent protein kinase (PKC) was clearly demonstrated in both the cytosolic and particulate fractions of immature Xenopus laevis oocytes and in the cytosolic fraction of mature oocytes. However, it was less active in metaphase II- than in prophase I-arrested oocytes. The enzyme was partially purified by DEAE-cellulose and phenyl-Sepharose chromatography. It was activated in vitro by the tumor-promoting phorbol ester, 12-O-tetradecanoyl phorbol 13-acetate (TPA) as already described for PKC from other tissues. On the other hand, a calcium-phospholipid-independent histone kinase activity 4-fold higher in metaphase II- than in prophase I-arrested oocytes was detected. The possible role of PKC and phospholipid-independent histone kinase in the maturation process is discussed.