Interaction of the GTP‐binding protein Gi2 with a protein kinase A‐like kinase in mouse fibroblasts

MICHAEL F. Crouch, DAVID A. Jans, LJUBOV Simson, IAN A. Hendry

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We have previously shown that the GTP‐binding protein, Gi2 of mouse Balb/c3T3 cells is linked to a serine kinase which phosphorylates the a‐subunit of Gi itself. In this report we show that Gi, is coupled to a second protein kinase. This kinase does not phosphorylate G, but phosphorylates another protein bound non‐covalently to Gi‐. Phosphorylation of the Gi‐linked protein induces its release from Gi. Kinase activity is slightly enhanced by G TPγS, suggesting that this kinase may be physiologically regulated by Gi. In an attempt to identify the kinase we have, examined the effect of peptide substrates and inhibitors on kinase activity. We found that the protein kinase A inhibitory peptide, PKI5‐24, inhibited the kinase activity, but at concentrations above those usually required to block protein kinase A. The protein kinase A substrate peptide, kemptide, acted as a substrate of the kinase, and was an inhibitor of the phosphorylation of the G‐linked protein. However, a protein kinase A, catalytic subunit antibody failed to react with any proteins linked to Gi. A protein kinase C inhibitory peptide had no effect on phosphorylation of the Gi‐linked protein. Thus, the identity of this kinase has not been resolved, but it may form part of the signalling system of activated Gi in fibroblasts.

Original languageEnglish
Pages (from-to)831-836
Number of pages6
JournalAustralian and New Zealand Journal of Medicine
Issue number6
Publication statusPublished - 1 Jan 1995
Externally publishedYes


  • G‐protein
  • mitosis
  • PKA
  • PKC
  • Signal transduction

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