Chicken Gizzard: Relation Between Calcium-Activated Phosphorylation and Contraction

Of the proteins in mechanically disrupted chicken gizzard fibers (no functional sarcolemma) only the 20,000-dalton light chains of myosin underwent large Ca2+-and Sr2+-dependent changes in phosphorylation. Phosphorylation closely corresponded with the Ca2+- and Sr2+-activated tensions. Adenosine 5'-O (3'-thiotriphosphate) only in the presence of Ca2+ induced irreversible Ca2+-insensitive activation of tension and thiophosphorylation of the 20,000-dalton light chains, and blocked incorporation of 32P from [gamma-32P]adenosine triphosphate into the myosin light chains.