In vivo phosphorylation of a synthetic peptide substrate of cyclic AMP-dependent protein kinase.

Abstract
A model synthetic peptide substrate of the cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase; EC 2.7.1.37), Leu-Arg-Arg-Ala-Ser-Leu-Gly, closely resembling the local phosphorylation site sequence in porcine hepatic pyruvate kinase, was phosphorylated in vivo after microinjection into Xenopus laevis oocytes. This result demonstrates that the microinjection technique, utilizing a synthetic peptide substrate, or possibly a synthetic substrate analog inhibitor can be used to study protein phosphorylation-dephosphorylation reactions in living oocytes. This follows, since it is clear that the injected peptide was accessible to the cellular compartment containing the protein kinase.

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