A specific phosphoprotein phosphatase acts on histone H1 phosphorylated by protein kinase C

A phosphohistone phosphatase from rat liver cytosol acts specifically on histone H1 that is phosphorylated with the Ca²⁺-phospholipid-dependent protein kinase (protein kinase C). The apparent K(m) for ³²P-labeled H1 is 1 μM; other histones or cytosolic proteins phosphorylated with protein kinase C or with cyclic AMP-dependent protein kinase are poor substrates for the phosphatase. The enzyme has been partially purified by gel-permeation chromatography and by utilizing a hih-performance liquid chromatography ion-exchange column. The physical properties of this enzyme include a Stokes radius of 5.0 nm, a sedimentation coefficient (s(20,w)) of 7.0 S, and a M(r) of 150,000. The detection of protein kinase as well as the specific phosphohistone phosphatase in purified rat liver nuclei suggests a physiologic role for a histone H1 phosphorylation-dephosphorylation cycle mediated gy protein kinase C and the corresponding phosphohistone phosphatase.