Protein kinase G

Protein Kinase G (PKG) is enzyme that catalyzes the transfer of phosphate from ATP to specific serine or threonine residues in proteins which turns their functions on or off in cell signalling cascades.

PKG is activated by cGMP (cyclic guanosine monophosphate) which enables it to phosphorylate a number of proteins in the smooth muscle (you may want to add more here).

PKG phosphorylates Myosin light chanin phosphatase which dephosphorylates the myosin light chains whose phosphorylation initiates smooth muscle contraction.