Non-receptor tyrosine kinases (nRTKs) are
cytoplasmic enzymes that are responsible for catalysing the transfer of a
phosphate group from a
nucleoside triphosphate donor, such as
ATP, to tyrosine residues in
proteins. Non-receptor tyrosine kinases are a subgroup of protein family
tyrosine kinases, enzymes that can transfer the phosphate group from ATP to a tyrosine residue of a protein (phosphorylation). These enzymes regulate many cellular functions by switching on or switching off other enzymes in a cell.