Protein kinase C beta (PKCβ) is unique among PKC isoforms in that a single gene locus encodes two proteins, PKCβI and PKCβII, that are generated by alternative splicing of C-terminal exons and have different physiological roles [10]. The difference between these two isoforms resides in the C-terminal V5 domains, although these still exhibit moderate homology in their amino acid sequences. Like other PKC isoforms, PKCβ contains two functional domains: an amino-terminal regulatory domain and a carboxyl-terminal catalytic domain (Fig. 1A). In the inactive state, the regulatory region is bound to the catalytic region and inhibits the activity of the enzyme. Dissociation of this intramolecular inhibitory interaction results in the activation of the enzyme.