Isolation of an inactive component from pig heart phosphoprotein phosphatase and its reassociation with an active...

Treatment of a pig heart phosphoprotein phosphatase (phosphoprotein phosphohydrolase, EC 3.1.3.16) of Mr 224 000 with 40% ethanol followed by gel-filtration on Sephadex G-150, dissociated the enzyme into an active component of Mr 31 000 and an inactive component of Mr 80 000. The inactive component reassociated with the active component, resulting in the formation of an enzyme form of Mr 123 000. A large excess of either component in the reassociation produced only this enzyme form. The ability of the inactive component to associate with the active component was lost by treatment of the inactive component with trypsin and heat (60 degrees C, 2 min) but not with DNAase and RNAase. Effects of the inactive component on the activities of the active component by the association were as followings. The inactive component: (1) stimulated slightly the 32P-H2B histone phosphatase activity in the presence of either NaCl or Mg(CH3COO)2 but inhibited strongly in the absence of the salts; (2) stimulated the 32P-H1 histone phosphatase activity in the presence of the salts; (3) inhibited the phosphorylase a phosphatase activity in the presence and absence of the salts; (4) enhanced the response to the stimulatory effects of the salts on the dephosphorylation of 32P-histone; and (5) protected the phosphorylase a phosphatase activity from inhibition by the salts.