In a previous communication (Li, H.-C., Hsiao, K.-J., and Chan, W. W. S. (1978) Eur. J. Biochem 84,215-225) we reported the purification of a divalent cation-independent, nonspecific phosphoprotein phosphatase (phosphatase S, M, = 35,000) from canine cardiac muscle to apparent homogeneity. It was found that the homogeneous enzyme preparation exhibited significant activity toward p-nitrophenyl p...