Characterization of a Phosphatase Specific for Phosphorylated Histones and Protamine

Abstract

Abstract A phosphatase which releases orthophosphate from histones and protamine has been purified 60-fold from rat liver. Histone phosphatase was detected by the use of substrates enzymatically phosphorylated by histone kinase. Purified histone phosphatase preparations are inactive in the dephosphorylation of other phosphoproteins, low molecular weight phosphate esters, and phosphopeptides derived from active substrates. The apparent Km for dephosphorylation of histone f1 is 2 x 10-5 m. The reaction products are orthophosphate and intact histone or protamine, as indicated by electrophoretic studies. Optimal reaction rates were observed at pH 7 to 8 and ionic strength 0.1 to 0.2. Chromatography on diethylaminoethyl cellulose resolved histone phosphatase activity into two fractions which exhibited a 2-fold difference in relative rates of dephosphorylation of histone fl and protamine. Histone phosphatase activity was detected in all eukaryotic cells examined, but it was absent in extracts of several prokaryotes.