The properties of purified low molecular weight phosphoprotein phosphatase from rabbit heart

Abstract

A simplified procedure for the purification of low molecular weight phosphoprotein phosphatase acting on muscle phosphorylase a has been described from rabbit heart. The enzyme was purified to homogeneity by acid precipitation, ethanol treatment, and chromatography on Sephadex G-75 and Sepharose–histone. The purified enzyme showed a single band when examined by sodium dodecyl sulfate – polyacrylamide gel electrophoresis; the molecular weight calculated by this method was 34 000. The S20,W value and Stokes radius for the enzyme was 3.35 and 24.0 Å (1 Å = 0.1 nm), respectively. Using these two values, a molecular weight of 35 000 was calculated. Purified enzyme showed a wide substrate specificity and catalyzed the dephosphorylation of phosphorylase a, glycogen synthase D, phosphorylated histone, and phosphorylated casein. Kinetic studies revealed the lowest Km with glycogen synthase D and maximum Vmax for the reaction with phosphorylase a.