Comparison of myosin light chain phosphorylation in uterine and arterial smooth muscles

1. The phosphorylatable light chain from uterine and arterial smooth muscles appear as four spots on two-dimensional gel electrophoretograms due to the existence of isoforms which may be non-, mono- or diphosphorylated. 2. The phosphorylation sites are serine and threonine residues; the phosphoserine to phosphothreonine ratio is smaller, and the extent of diphosphorylation is larger in uterus than in artery. 3. Different phosphorylation values found at identical tension levels and identical phosphorylation values found at different tension levels narrow the role of light chain phosphorylation to the activation of smooth muscle contraction.