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 13 000 M r enzyme. Purification of the second form by affinity chromatography on calmodulin-Sepharose showed it to consist of two polypeptide chains of M r 136 000 and 141 000. This form of the enzyme required Ca 2+ and calmodulin for activity, was specific for the M r 20 000 light chain of myosin, and appeared to phosphorylate the same site on the light chain as the M r 130 000 enzyme. The low- M r gizzard kinase may be a proteolytic fragment of a higher- M r species or these may represent different isoenzymes.