The cytosolic phosphorylase kinase complex catalyzes the phosphorylation of the subunits of the glycogen phosphorylase (PYGM) dimer. Two forms of phosphorylase kinase complex have been described (Brushia and Walsh 1999). The one annotated here, consisting of four copies each of PHKA1 (alpha regulatory) (Burwinkel et al 2003), PHKB (beta regulatory) (Burwinkel et al. 2003), PHKG1 (gamma catalytic) (Burwinkel et al. 2003) and CALM (calmodulin) subunits is abundant in muscle and its action on the form of phosphorylase (PYGM) abundant in muscle is described.
While initial studies of PGYM from rabbit muscle suggested that it is a homotetramer (Keller and Cori 1953), more recent work indicates that under physiological conditions the enzyme occurs as a homodimer (Huang and Graves 1970) and a dimeric structure for the human enzyme is inferred here.