Bovine liver phosphoamidase as a protein histidine/lysine phosphatase

A 13-kDa phosphoamidase was isolated as a single band on SDS-PAGE from bovi ne liver, Its Stokes' radius, sedimentation coefficient, molecular mass, an d optimal pH were estimated to be 1.6 nm, 1.8 s, 13 kDa, and 6.5, respectiv ely. The enzyme released P-i from 3-phosphohistidine, 6-phospholysine, and amidophosphate at rates of 0.9, 0.6, and 2.6 mu mol/min/mg protein, respect ively. However, it did not dephosphorylate phosphocreatine, N-omega-phospho arginine, imidodiphosphate, or O-phosphorylated compounds including inorgan ic pyrophosphate. It also dephosphorylated succinic thiokinase and nucleosi de diphosphate kinase autophosphorylated at His residues, indicating that i t works as a protein histidine phosphatase. A thiol reagent, 30 mu M N-ethy lmaleimide, depressed the activity by half, while a thiol compound, 2-merca ptoethanol, protected the enzyme from heat-inactivation. Five millimolar di valent cations, such as Mg2+ and Mn2+, and 5 mM EDTA, had no effect on the activity.