120 ALEXANDER L. DOUNCE 



II. Chemical Composition of the Cell Nucleus 

 1. Introductory Remarks 



If one were to review uncritically the literature pertaining to the compo- 

 sition of cell nuclei, a rather impressive table of results could be compiled, 

 some of which would however be highly contradictory and many of which 

 would be of little or no significance. This is because many workers have 

 given scant attention to the effects of the method of isolation of nuclei on 

 the final composition of the purified nuclei. Thus, it is easy to find results 

 showing the DNA concentration of mammalian liver cell nuclei to be 30 % or 

 higher, but such a high figure indicates only that much protein has been 

 lost from the nuclei during the isolation procedure. It has been particularly 

 difficult to arrive at a correct interpretation of the results obtained from 

 analyzing cell nuclei for enzymes. 



The following material on the composition of the cell nucleus has been 

 assembled with due regard to probable distortions caused by the isolation 

 procedures and accordingly some data recorded in the literature have not 

 been included. In certain cases where it is impossible to decide which of two 

 or more conflicting values is correct, all available data are listed together 

 with the corresponding references. 



2. Composition of the Nucleus with Respect to Lipid 

 a. Total Lipid 



The total lipid of rat liver nuclei has been determined by several investi- 

 gators. Using rats of the Osborne-Mendel strain, the writer found 3.2% 

 total hpid in the nuclei prepared at pH 4 and 7.5% in the pH 6 nuclei.* 

 Using rats of the Wistar strain, about 6.3% lipid was found in the pH 4 

 nuclei and about 10.8 % in the pH 6 nuclei. Whether the difference between 

 the two strains is of biochemical significance is not known, but the differ- 

 ences between nuclei isolated at pH 4 and pH 6 seem to be real, although 

 of unknown cause. Possibly there is less adsorption of fine mitochondrial 

 fragments by the pH 4 nuclei, but it is quite likely that a real variation in 

 lipid content occurs, since the per cent DNA is about the same for nuclei 

 isolated at pH 6.0 and pH 4.0,'^ indicating a similar protein content for both 

 types of nuclei. In this work the lipid was extracted by means of a hot 

 alcohol-ether mixture followed by a chloroform-methanol mixture, and all 

 the extracted material, after evaporation of the solvents, was found to be 

 soluble in petroleum ether. Hence, it is unlikely that differences in firmness 

 of binding of the lipid to nuclear material influenced the results. 



Total lipid has also been estimated by WiUiams et al.^^ for rat and dog 



«» H. H. Williams, M. Kaucher, A. J. Richards, and E. Z. Moyer, /. Biol. Chem. 160, 

 227 (1945). 



