Histones with High L¥sine Content by M. M. Daly and A. E. Mirsky

This paper deals with some basic proteins of cell nuclei which differ in a number of ways from the classical histones of Kossel. Two characteristics of a histone noted by Kossel are its high arginine content and its way of being precipitated on addition of an excess of ammonium hydroxide (1-2). A high arginine content would tend to give a protein a basic isoelectric point and precipitability in ammonium hydroxide is also evidence of a basic isoelectric point. That a histone actually has a basic isoelectric point is shown by its being precipitated at about pH 10.6 by addition of sodium hydroxide and by its redissolving when an excess of alkali is added (3). In Kossel's time an excess of hydrochloric or sulfuric acid was always used to free a histone from its combination with desoxyribonucleic acid and it might be thought that the insolubility of a histone at its isoelectric point should be attributed to the denaturing effect of treatment with strong acid. More recently, however, histone has been dissociated from nucleic acid by a high concentration of sodium chloride at neutrality and then separated from the nucleic acid by high speed centrifugation, which sediments the nucleic acid, leaving histone in the supernate (3). Histone prepared in this way was also found to be insoluble at its isoelectric point so that there is no reason to attribute this property to denaturation. The basic proteins to be described in this paper are, like the classical histones, derived from the cell nucleus but differ from them in having a low arginine content, an exceedingly high lysine content, and in being soluble in the isoelectric region. We first prepared these lysine-rich proteins nearly 3 years ago and most of their properties which we shall describe were already noted then. On looking over the older literature at that time we noted that lysine-rich material having much in common with the substances which we were preparing had already been described by Felix in 1921 (4). The next paper on this subject was by Kossel and Schenk in 1928 (5). In this paper a "cyprinodipeptone" prepared from the testes of the carp was described. Analysis showed that 46.80 per cent of the nitrogen of this substance was lysine nitrogen and 0.36 per cent was arginine nitrogen. We have returned to this subject during the past year because exper~nents on N is uptake and retention have shown that the synthesis of histone (and here we mean the protein isolated by precipitation at pH 10.6) is in some 4O5