Purification of gizzard myosin light-chain phosphatase, and reversible changes in the ATPase and superprecipitation activities of actomyosin in the presence of purified preparation of myosin light-chain phosphatase and kinase.

Sepharose 4B conjugated with phosphorylated myosin light chains was used in affinity chromatography of a partially purified preparation of gizzard myosin light-chain phosphatase (MLCP) (Onishi et al. (1979) J. Biochem. 86, 1283-1290). The MLCP preparation thus purified contained, according to SDS gel electrophoresis, three components of 67,000 (67 K), 54,000 (54 K), 34,000 (34 K) daltons. In an accompanying report, Uchiwa et al. (J. Biochem. 91, 273-282 (1982)) described the purification of gizzard myosin light-chain kinase, which consisted of two subunits; 130 K and 17 K daltons. Using the purified preparations of MLCP and MLCK, it was demonstrated a) that reversible changes in the ATPase and superprecipitation activities occur as myosin light chains are enzymatically phosphorylated and dephosphorylated, and b) that addition of a very low concentration of Ca2+ and its removal cause reversible changes in the turbidity of actomyosin suspensions as well as in the state of phosphorylation of myosin light chains only when MLCK and MLCP are both present. These results provide strong support for the proposal (see Ikebe et al. (1977) J. Biochem. 80, 299-302) that MLCK and MLCP play a key role in the Ca2+ regulation in gizzard.