Phosphorylase b kinase catalyzes the phosphorylation of serine in certain substrates, including troponin I. The beta chain acts as a regulatory unit and modulates the activity of the holoenzyme in response to phosphorylation (By similarity). Glycan biosynthesis; glycogen metabolism. Although the final Cys may be farnesylated, the terminal tripeptide is probably not removed, and the C-terminus is not methylated. Belongs to the phosphorylase b kinase regulatory chain family.