The cytosolic phosphorylase kinase complex catalyzes the phosphorylation of glycogen phosphorylase (PYGL). Two forms of phosphorylase kinase complex have been described (Brushia and Walsh 1999). The one annotated here, consisting of four copies each of PHKA2 (alpha regulatory) (van den Berg et al. 1995), PHKB (beta regulatory) (Burwinkel et al. 2003a), PHKG2 (gamma catalytic) (Burwinkel et al. 2003b; Maichele et al. 2006) and CALM (calmodulin) subunits is abundant in liver and its action on the form of phosphorylase (PYGL) abundant in liver is described.
While initial studies of glycogen phosphorylase 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 human PYGL enzyme is inferred here.