PKC (Protein kinase C) is a family of protein kinase enzymes that are involved in controlling the function of otherproteins through the phosphorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins. PKC enzymes in turn are activated by signals such as increases in the concentration of diacylglycerol (DAG) or calcium ions (Ca2+). Hence PKC enzymes play important roles in several signal transduction cascades. The PKC family consists of 15 isozymes in humans: PKC-α (PRKCA), PKC-β1 (PRKCB), PKC-β2 (PRKCB), PKC-γ (PRKCG), PKC-δ (PRKCD), PKC-δ1 (PRKD1), PKC-δ2 (PRKD2), PKC-δ3 (PRKD3), PKC-ε (PRKCE), PKC-η (PRKCH), PKC-θ (PRKCQ), PKC-ι (PRKCI), PKC-ζ (PRKCZ), PK-N1 (PKN1), PK-N2 (PKN2), PK-N3 (PKN3). PKC is involved in receptor desensitization, in modulating membrane structure events, in regulating transcription, in mediating immune responses, in regulating cell growth, and in learning and memory. These functions are achieved by PKC-mediated phosphorylation of other proteins.