Characterization of nuclear phosphoprotein phosphatases from goat testis

Two nuclear phosphoprotein phosphatases (PPases I and II) that cause dephosphorylation of [32P]histone, have been partially purified from goat testis. The enzymic activity is associated with nucleoplasm and chromatin. PPase I is markedly stimulated (approx. 200-600%) by Mg2+ or Mn2+ (1 mM) whereas Ca2+ (1 mM) causes slight stimulation (approx. 35%) of the enzyme. On the contrary, PPase II is only slightly activated (20-40%) by these metal ions (5 mM). Both the phosphoprotein phosphatase isoenzymes are maximally active at pH 6-7. PPases I and II are strongly inhibited (approx. 60-100%) by ZnCl2 (1 mM), P1 (5 mM) and thiol reagents. NaF (5 mM) inhibits (approx. 40%) specifically the activity of PPase I rather than PPase II. PPases are strongly inhibited by relatively high concentration of NaCl (0.4 M), isoenzyme II being more sensitive (approx. 80%) than isoenzyme I (approx. 50%). In addition to histones, both the isoenzymes can as well cause dephosphorylation of protamine, casein, and testicular nuclear proteins. Enzymic characteristics of the testicular nuclear PPases are clearly different from those of the cytosolic enzyme previously characterized.