The enzyme (EC 22.214.171.124) that integrates the hormonal and calcium signals in muscle and regulates the activity of glycogen phosphorylase and glycogen synthetase by addition of phosphate groups. A large and complex enzyme, itself regulated by phosphorylation, consisting of four copies of an α-β-γ-δ tetramer with several isoforms of the α, β, and γ subunits. The α (1235 aa) and β (1093 aa) subunits have regulatory functions, the γ subunit (406 aa) has the catalytic activity, the δ subunit is calmodulin. Mutations lead to X-linked liver glycogenosis (glycogen storage disease type IXa, GSDIXa). X-linked muscle phosphorylase kinase deficiency (GSDIXd) is caused by mutation in the gene encoding the α subunit. Autosomal recessive liver glycogenosis (GSDIXc) is caused by mutation in the γ2 isoform.
Subjects: Medicine and Health.