Phosphorylase b kinase catalyzes the phosphorylation of serine in certain substrates, including troponin I. Polymer of 16 chains, four each of alpha, beta, gamma, and delta. Alpha and beta are regulatory chains, gamma is the catalytic chain, and delta is calmodulin. The two calmodulin-binding domains appear to act in concert to bind a single molecule of calmodulin and are pseudosubstrate/autoinhibitory domains.
