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Phosphorylase kinase (PhK) is a serine/threonine-specific protein kinase which activates glycogen phosphorylase to release glucose-1-phosphate from glycogen.PhK phosphorylates glycogen phosphorylase at two serine residues, triggering a conformational shift which favors the more active glycogen phosphorylase "a" form over the less active glycogen phosphorylase b.
Phosphorylase b kinase regulatory subunit alpha, liver isoform is an enzyme that in humans is encoded by the PHKA2 gene. [5] [6] References
Dihydroxyacetone kinase in complex with a non-hydrolyzable ATP analog (AMP-PNP). Coordinates from PDB ID:1UN9. [1]In biochemistry, a kinase (/ ˈ k aɪ n eɪ s, ˈ k ɪ n eɪ s,-eɪ z /) [2] is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates.
It was found that an enzyme, named phosphorylase kinase and Mg-ATP were required to phosphorylate glycogen phosphorylase by assisting in the transfer of the γ-phosphoryl group of ATP to a serine residue on phosphorylase b. Protein phosphatase 1 is able to catalyze the dephosphorylation of phosphorylated enzymes by removing the phosphate group.
Phosphorylase a is the more active R form of glycogen phosphorylase that is derived from the phosphorylation of the less active R form, phosphorylase b with associated AMP. The inactive T form is either phosphorylated by phosphoylase kinase and inhibited by glucose, or dephosphorylated by phosphoprotein phosphatase with inhibition by ATP and/or ...
Glycogen phosphorylase kinase activates glycogen phosphorylase in the same manner mentioned previously. Glycogen phosphorylase b is not always inactive in muscle, as it can be activated allosterically by AMP. [6] [9] An increase in AMP concentration, which occurs during strenuous exercise, signals energy demand. AMP activates glycogen ...
Phosphorylase b kinase gamma catalytic chain, testis/liver isoform is an enzyme that in humans is encoded by the PHKG2 gene. [5] [6] [7] The PHKG2 gene provides instructions for making one piece, the gamma subunit, of the phosphorylase b kinase enzyme. This enzyme is made up of 16 subunits, four each of the alpha, beta, gamma, and delta subunits.
Epinephrine not only activates glycogen phosphorylase but also inhibits glycogen synthase. This amplifies the effect of activating glycogen phosphorylase. This inhibition is achieved by a similar mechanism, as protein kinase A acts to phosphorylate the enzyme, which lowers activity. This is known as co-ordinate reciprocal control.