Action of Adenosine 3',5'-Monophosphate-dependent Histone Kinase in Vivo

An adenosine 3',5'-monophosphate-dependent protein kinase preparation from liver catalyzes the phosphorylation of a specific serine residue in lysine-rich (f1) histone. Evidence, based on the isolation of electrophoretically and chromatographically identical tryptic phosphopeptides from f1 histone phosphorylated in vivo and in vitro, indicates that phosphorylation of this serine residue occurs in rat liver in vivo and is increased 8- and 20-fold, respectively, by intraperitoneal injections of adenosine 3',5'-monophosphate and N6,O2'-dibutyryl cyclic AMP. Thus histones appear to serve as substrates in vivo for the adenosine 3',5'-monophosphate-dependent protein kinase of liver.