FIG. 2.

Absence of PKI activity in PKIα knockout skeletal muscle. Heat-inactivated tissue extracts from wild-type (WT) and PKIα knockout (KO) skeletal muscle were added to an assay measuring phosphorylation of the PKA substrate, kemptide, by exogenous PKA (C subunit). Kinase activity is expressed as a percentage of the control, where 100% represents kinase activity in the absence of any added tissue extract. The PKI present in wild-type muscle extract almost completely inactivates PKA. Extracts from PKIα knockouts have no significant effect even at the highest concentration of protein, demonstrating a complete absence of PKI activity in PKIα-null skeletal muscle. The error bars represent standard errors of the mean.