A Protein-Bound Polysaccharide from Basidiomycetes Enhances Myosin Phosphorylation but Inhibits Myosin ATPase Activity: Studies with a Crude Actomyosin Preparation of Chicken Gizzard Smooth Muscle

Abstract

Chicken gizzard actomyosin, containing the calmodulin-myosin light chain kinase (MLCK) system, was incubated in the presence of various concentrations of PSK, a protein-bound polysaccharide from Basidiomycetes, together with Ca²⁺ and Mg-ATP. The phosphoryla-tion of myosin was enhanced half-maximally by 10^-4 g/ml of PSK. However, a similar concentration of PSK reduced the Mg-ATPase activity of the actomyosin. The former was brought about through stimulation of the MLCK activity and the latter through inhibition of the myosin ATPase activity.