Purification of Myosin Light Chain Kinase from Rabbit Polymorphonuclear Leukocytes

Abstract

Pediatr. Res. 15: 229-234 (198 The crude cofactor preparations isolated from the two types of leukocyte extracts were interchangeable with the leukocyte myosins. When ALM cofactor was added to a P M N actomyosin complex, the Mg"-ATPase activity of the P M N myosin was 3-fold higher than with ALM cofactor and its own actomyosin complex. In contrast, PMN cofactor did not enhance ALM actomyosin Mg++-ATPase activity beyond that observed with ALM cofactor and ALM actomyosin. Cofactor protein from the PMN was further purified on a DEAE-Sephagel column. After electrophoresis on sodium dodecyl sulfate-polyacrylamide gel, the isolated fraction weighed 70,000 daltons. This fraction stimulated the actinmediated myosin Mg++-ATPase. In the presence of Mg++ and ly32PJATP, the 70,000 dalton protein phosphorylated the 20,000 dalton light chain of PMN myosin, leading to the incorporation of 0.62 + 0.09 moles of Pi per mole myosin. O n the basis of these results, we propose that phagocytic cofactor is a kinase which regulates the enzymatic activity of phagocytic cell myosin.