130 ALEXANDER L. DOUNCE 



An extensive study of the histone content of whole cell nuclei has re- 

 cently been made by Stedman and Stedman.^"^^ Their data show values 

 for histone sulfate ranging from 17 to slightly more than 30% for various 

 types of cell nuclei isolated in 4% acetic acid solution. These results may 

 be valid for the type of preparation in question, but no allowance has been 

 made for a possible partial loss of histone and a certain loss of much non- 

 histone protein during the isolation procedure, since the Stedmans do not 

 believe that any such loss occurs. Nevertheless, the high DNA content of 

 their cell nuclei constitutes direct evidence of loss of much protein. Un- 

 fortunately many of the conclusions drawn by the Stedmans from their 

 experimental data, however excellent the latter may be, are, in the opinion 

 of the writer, highly questionable. 



It has been demonstrated^ that an increasing loss of protein from nuclei 

 occurs as the pH is lowered below 4.0. It was thought at one time that the 

 extracted protein was mainly histone, but this is not necessarily true, al- 

 though it is likely that at low pH values at least some histone is lost. 

 Therefore, it is difficult or impossible to apply a correction factor to the 

 Stedmans' results to allow for the probable effect of strong acid in reducing 

 the percentage of histone in the nuclei. Recent analyses of rat liver cell 

 nuclei isolated at pH 4.0 in the writer's laboratory have shown a histone 

 content of about 17 to 20%. 



/. Protamine Content of Nuclei of Spermatozoa. The basic protein of fish 

 sperm nuclei is protamine. This low-molecular-weight basic protein, which 

 unlike histone can be slowly dialyzed through a collodion membrane,^"* 

 comprises a large fraction of the nucleus, but just how large is still uncer- 

 tain. The older workers thought that nucleoprotamine comprised about 

 81 % of the lipid-free sperm cell nucleus. Mirsky and Pollister^'^^ found an 

 even higher amount (about 91 %) but called attention to the probable im- 

 portance of the remaining nonprotamine protein. From data in this refer- 

 ence^"^ and from that in an earlier paper of Mirsky and Pollister,!"^ it can 

 be calculated that trout sperm nuclei contain around 63% protamine. 

 Owing to the fact that spermatozoa nuclei have been isolated only in 

 aqueous media, values of the content of various protein fractions are not 

 kno^\'Ti with very great certainty. 



g. Content of Acidic Lipoprotein {Residual Protein). According to Mayer 

 et a/.,^'"' the liproprotein fraction of cell nuclei isolated from rat liver in very 

 dilute citric acid at pH 6.0 amounts to about 50% by dry weight of these 



lo^D. Hamer, Brit. J. Cancer 7, 151 (1953). 



'«' M. M. Daly, A. E. Mirsky, and H. Ris, J. Gen. Physiol. 34, 439 (1951). 



'»'" E. Stedman and E. Stedman, Phil. Trans. Roy. Soc. (London) B235, 565 (1951). 



i»« A. E. Mirsky and A. W. PoUister, J. Gen. Physiol. 30, 101 (1946). 



109 A. E. Mirsky and A. W. Pollister, Proc. Natl. Acad. Sci. U.S. 28, 344 (1942). 



