Salt stimulation of the activation of latent protein phosphatase, Fc.M, by Mn++ and by Mn/trypsin.

The activation of porcine heart latent protein phosphatase (Fc.M) by pretreatment with Mn++ followed by trypsin (Mn/trypsin) can be stimulated 2.5-fold by including NaCl or KCl in the activation mixtures. The salts also stimulated the activation of the enzyme by Mn++ to the same level as that obtained by Mn/trypsin pretreatment in the absence of salt. The presence of salt in both the Mn++ and Mn/trypsin activations decreased the Mn++ requirement 10-fold in each case. Treatment of latent Fc.M by Mn/trypsin in the presence of 0.2 M NaCl or KCl offers a convenient method of expressing the full potential activity of the protein phosphatase.