TYROSINE PHOSPHORYLATION OF PROTEIN-KINASE C-DELTA IN RESPONSE TO THE ACTIVATION OF THE HIGH-AFFINITY RECEPTOR FOR IMMUNOGLOBULIN-E MODIFIES ITS SUBSTRATE RECOGNITION

The delta isoform of protein kinase C is phosphorylated on tyrosine in response to antigen activation of the high-affinity receptor for immunoglobulin E, While protein kinase C-delta associates with and phosphorylates this receptor, immunoprecipitation of the receptor revealed that little, if any, tyrosine-phosphorylated protein kinase C-delta is receptor associated, rn vitro kinase assays with immunoprecipitated tyrosine-phosphorylated protein kinase C-delta showed that the modified enzyme had diminished activity toward the receptor gamma-chain peptide as a substrate but not toward histones or myelin basic protein peptide. We propose a model in which the tyrosine phosphorylation of protein kinase C-delta regulates the kinase specificity toward a given substrate, This may represent a general mechanism by which in vivo protein kinase activities are regulated in response to external stimuli.