Experimental Gerontology, Vol. 17, pp. 359-364, 1982 0531-5565/82/050359-06503.00/0 Printed in the USA. All rights reserved. Copyright © 1983 Pergamon Press Ltd AGE CHANGES OF THE ISOELECTRIC POINTS OF NON-HISTONE CHROMOSOMAL PROTEINS FROM RAT LIVER IN THE pH RANGE 5 to 8 AUREL POPA WAGNER,* EUGENIA PSARROU,** AND LISELOTTE POPA WAGNER'~ (Received 2 November 1981) INTRODUCTION IT IS generally believed that the biological aging process has a genetic determinant, i.e., ag- ing is a part of the developmental program inscribed in the genetic material, DNA (Mor- row & Garner, 1979). Hence, the attention paid to chromatin and its components: DNA, histones, non-histone chromosomal proteins (NHC proteins). It is also believed that chromatin activity is modulated by NHC proteins which are highly heterogenous, acidic and tissue-and species-specific (Barrett & Gould, 1973) being implicated in gene expression in general (Stein et aL, 1974) and in the control of transcrip- tion in particular (Wang & Kostraba, 1975; Nguyen et al., 1975). NHC proteins undergo also covalent modifications like phosphorylation and acetylation (Liew & Gornall, 1975) which are in turn, modulated by calcium and estradiol in an age-dependent process (Kanungo & Thakur, 1979). In addition, there are reports about discrete variations with age among several specific proteins in rat liver nuclei of different ploidy (Garker & Brasch, 1979) and in human doploid fibroblasts (Dell'Orco et al., 1978). In literature there are some reports dealing with the isoelectric points of NHC proteins extracted from rat liver (Mac Gillivray & Rickwood, 1974; Gronow & Thackrah, 1978; Dayal et aL, 1979; Legraverend & Glazer, 1980) but the results can hardly be compared as the authors used a variety of extraction and isoelectric focusing methods. However, in our review on the literature, we did not find any relevant paper concerning isolectric points of NHC proteins in ageing rat liver. In the present article, we focused our attention on age- related changes in the isoelectric points of NHC proteins in the pH range 5-8. *Cartier 1 Mai, BI.I 61, Ap. 10, Craiova 1100, Romania **Address for correspondence: Eugenia Psarrou, Meidani 8, Kukaki, Atena, Greece tInstitute of Biological Sciences, Splaiul Independentei N ° 296, Bucharest, R-77748, Romania 359