Identification of two forms of myosin light chain kinase in turkey gizzard

Two forms of myosin light chain kinase from turkey gizzard are separable by ion-exchange chromatography. One is the well-characterized 130,000 Mr enzyme. Purification of the second form by affinity chromatography on calmodulin--Sepharose showed it to consist of two polypeptide chains of Mr 136,000 and 141,000. This form of the enzyme required Ca2+ and calmodulin for activity, was specific for the Mr 20,000 light chain of myosin, and appeared to phosphorylate the same site on the light chain as the Mr 130,000 enzyme. The low-Mr gizzard kinase may be a proteolytic fragment of a higher-Mr species or these may represent different isoenzymes.