Recombinant protein segments from a metabotropic glutamate receptor and from anodorantreceptor were used as substrates in protein kinase C phosphorylation assays. Protein kinaseCβand δ phosphorylated an intracellular consensus phosphorylation site in the metabotropicglutamatereceptor. Only protein kinase C δ phosphorylated a novel extracellular consensusphosphorylationsitein the odorant receptor. These results suggest differential regulation of these receptors by proteinkinaseC isotypes.