title: In vitro studies on the methylation of histones in rat brain nuclei.
abstract: When isolated nuclei from 12-day-old rat brains were incubated with S-adenosyl-L-[methyl-3H]methionine, significant amounts of 3H-methyl were incorporated into lysyl residues in histones H3 and H4. About 0.024% of the total methylation sites on histone H3 and 0.013% of the sites on histone H4 were unmethylated at the time the nuclei were isolated. Methylation of these sites proceeded stepwise, progressing to a stable ratio of 0.93:1.0:0.17 for N epsilon-mono-, N epsilon-di-, and N epsilon-trimethyllysine in histone H3 and 0.19:1.0 for N epsilon-mono- and N epsilon-dimethyllysine in histone H4. The Km values of the enzyme for S-adenosyl-L-methionine were 11.5 +/- 1.1 micron and 12.5 +/- 1.3 micron with histones H3 and H4 as methyl acceptors, respectively. The Vmax values were 11.1 and 5.3 pmol of 3H-methyl incorporated/min/mg of histone H3 and H4, respectively. Since histone H3 contains 2 mol of N epsilon-methyllysine/mol and histone H4 contains 1 mol/mol, no difference in the overall rates of methylation can be deduced from the data. S-Adenosyl-L-homocysteine, one of the products of the reaction, was a competitive inhibitor with respect to S-adenosyl-L-methionine. The Ki values for S-adenosyl-L-homocysteine were 5.5 +/- 0.4 micron and 5.9 +/- 0.5 micron with histones H3 and H4 as methyl acceptors, respectively.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000201:enzymology*; D002467:Cell Nucleus / Q000201:enzymology*; D011495:Histone-Lysine N-Methyltransferase / Q000378:metabolism*; D006657:Histones / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D011496:Protein Methyltransferases / Q000378:metabolism*; D051381:Rats; D012435:S-Adenosylhomocysteine / Q000494:pharmacology
chemical_list: D006657:Histones; D012435:S-Adenosylhomocysteine; D011496:Protein Methyltransferases; D011495:Histone-Lysine N-Methyltransferase