Age-related effects on the incorporation of acetate into rat liver histones

Incorporation of sodium [3H]acetate into histones of rats was examined as a function of age. Incorporation was observed to decline with age up to 24 months, at which time a levelling occurred. Controls indicated that this decrease in histone acetylation could not be attributed to variability in isotope delivery to the liver or to alterations in intracellular 'pools' available for acetylation. Polyacrylamide gel electrophoresis established that, in all cases, acetate was incorporated primarily into histone fractions H3 and H4 and the pattern of incorporation exhibited age-dependent phenomena. H4 was predominantly labelled in 2 months animals, while in 12, 16, and 24 months animals H3 was more highly labelled; at 27 months the two fractions were labelled equally. Assessment of histone acetylase and deacetylase activities indicates that deacetylase activity increased with age.