Protein Kinase (PK)

A protein kinase is an enzyme that selectively modifies other proteins by covalently attaching phosphate groups to them—a process known as phosphorylation. This modification typically occurs on specific amino acids with free hydroxyl groups, most commonly serine, threonine, or tyrosine residues. Phosphorylation often results in a functional change of the target protein (the substrate), affecting its enzymatic activity, cellular localization, or interactions with other proteins. Protein kinases are central regulators of cellular pathways and signal transduction. They control diverse processes such as cell growth, differentiation, metabolism, apoptosis, gene expression regulation, mitosis, and responses to external stimuli. In humans alone there are about 500 protein kinase genes—about 2% of all human genes—and up to 30% of all human proteins may be modified by kinase activity.

Inhibition of phosphorylation