Insulin and progesterone activate a common synthetic ribosomal protein S6 peptide kinase in Xenopus oocytes

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Abstract
A synthetic peptide Arg‐Arg‐Leu‐Ser‐Ser‐Leu‐Arg‐Ala, the structure of which is based on that of a phosphorylated sequence in ribosomal protein S6, was employed as a probe for stimulated kinase activity in Xenopus laevis oocytes induced to mature with insulin or progesterone. Insulin elicited an early (20–30 min) 3‐fold stimulation of S6 peptide phosphorylating activity that was not evident with progesterone. However, both hormones produced a delayed 7–12‐fold stimulation of S6 peptide phosphorylating activity at the time of germinal vesicle breakdown. The results of DEAE‐Sephacel, Sephacryl S‐200, TSK‐400, and heparin‐Sepharose chromatographic fractionation experiments imply that a common S6 peptide kinase is activated as a consequence of short and long term insulin exposure, as well as in long term progesterone treatment of oocytes. Omission of potassium from the oocyte culture medium greatly facilitated insulin‐induced meiotic maturation.