Protein kinase C forms a complex with and phosphorylates the GTPase activating protein GAP: phosphorylation by PKC is dependent on tyrosine phosphorylation of GAP and/or a GAP-associated protein.

Protein kinase C (PKC) and the GTPase-activating protein GAP can be detected in immunoprecipitates of mouse epidermis and lung cytosol obtained with either anti-GAP or anti-PKC antisera. The PKC in the immune-complex phosphorylates the coprecipitated GAP protein. Moreover, purified recombinant GAP is phosphorylated in vitro by purified PKC. The efficacy of this phosphorylation appears to depend on the extent of tyrosine phosphorylation of GAP and/or a GAP-associated protein.