[In vitro-phosphorylation of histones in chromatin of various tissues in relation to age (author's transl)].

The influence of age on the structure of chromatin of various mammalian cells with modest or terminated mitotic activity has been examined. For this purpose chromatin from dog skeletal muscle, and human neuronal and glial cells, has been incubated together with an exogenous histone phosphokinase and ATP-gamma32P, and the phosphate incorporated into the histones determined. For comparison, also free histone has been phosphorylated. The amount of phosphate incorporated into total histone is 16-18 nmol Pi per mg histone in the case of free histone, and about equal for all cell types and ages. Into chromatin-bound histones only 5.5-8.2 nmol Pi per mg histone are incorporated. The differences between the various cell types and age groups are not significant. The relative phosphate incorporation into the single histone fractions depends on the histone as being free or chromatin-bound. In addition, relative phosphate incorporation into the single fractions of chromatin-bound histones is also cell type- and age-specific. The results permit the conclusion that the chromatin is subject to structural changes in the course of aging.