Phosphorylase b Kinase (PhK)

Phosphorylase b kinase (PhK) is a large, multi-subunit serine/threonine-specific protein kinase that plays a central role in glycogen metabolism. Its primary function is to activate glycogen phosphorylase by phosphorylation, thereby initiating the breakdown of glycogen into glucose-1-phosphate. The holoenzyme consists of 16 subunits arranged as four copies each of alpha (α), beta (β), gamma (γ), and delta (δ) subunits. The γ subunit provides the catalytic activity, while the α, β, and δ subunits are regulatory; the δ subunit is identical to calmodulin and binds calcium ions. PhK activity is tightly regulated through allosteric regulation by calcium ions, covalent modification by PKA-mediated phosphorylation, and autophosphorylation. It is highly expressed in liver and muscle cells, supporting immediate energy needs during contraction and maintaining blood glucose levels. Defects in any component can lead to metabolic disorders affecting energy balance.

Other names

Phosphorylase kinasePHKphosphorylase b kinase (PHK)

Phosphorylation of glycogen phosphorylase b to activate it.