ISOLATION AND COMPOSITION OF NUCLEI AND NUCLEOLI 141 



chromosomal protein are, as far as is known, confined to the cell nucleus is 

 evidence that enzymes of protein synthesis must be present within the cell 

 nucleus. 



6. Composition with Respect to Vitamins and Coenzymes 



For the study of water-soluble vitamins and coenzymes, it seems certain 

 that the Behrens-type nuclei should be used. Some work has been done by 

 Lang et al.^^ on the vitamin B12 content of liver cell nuclei, but here nuclei 

 isolated in aqueous media were used, and the results, showing a lower con- 

 centration of B12 in the nuclei than in the cytoplasm, cannot be considered 

 as valid without confirmation by work unth the Behrens-type nuclei. Wil- 

 liams et al}*^ investigated a number of vitamins in various types of cell 

 nuclei isolated by means of the Behrens procedure, but the method of dry- 

 ing the tissue in the opinion of the writer was so unsatisfactory that diffu- 

 sion artifacts may well have invalidated the results. 



Coenzyme I is generally scarce in or absent from nuclei isolated in aque- 

 ous media, but Stern and Mirsky'" have found this coenzyme in consider- 

 able concentration in liver cell nuclei isolated by the Behrens procedure. 



For a study of fat-soluble vitamins or coenzymes, nuclei isolated in aque- 

 ous media should be used, but thus far no such studies seem to have been 

 made. Bounce and Lan'^« found xanthophyll in nuclei of chicken erythro- 

 cytes. 



7. Composition with Respect to Minerals 



Bounce and Beyer^ have published results on the metal content of nuclei 

 isolated in dilute citric acid, and Lang et al}''"' have done similar work on 

 the metal content of nuclei isolated in strong sucrose solution. The results 

 of the studies are somewhat discordant, but in neither case can they be 

 considered as reliable indications of the amount of metal in the nucleus 

 as it exists within the living cell, since aqueous solvents were used in the 

 isolation procedure. The zinc content of tumor nuclei (also isolated in aque- 

 ous media) has been studied by Heath and Liquier-Milward.^^^ Poulson 

 and Bowen'^' have reviewed the histochemical localization of various metals 

 in cell nuclei. 



The presence of calcium or magnesium or both in cell nuclei has been re- 

 ported by Scott, ^^o who used emission electron microscopy on sections ob- 



1^5 E. R. Isbell, H. K. Mitchell, A. Taylor, and R. J. Williams, Univ. Texas Puhl. 



No. 4237, 81 (1942). 

 1" A. L. Bounce and T. H. Lan, Science 97, 584 (1943). 

 1" G. Siebert, K. Lang, and H. Lang, Biochem. Z. 321, 543 (1951). 

 "8 J. C. Heath and J. Liquier Milward, Biochim. el Biophys. Acta 5, 404 (1950). 

 "9 D. G. Poulson and V. T. Bowen, Exptl. Cell Research Suppl. 2, 161 (1952). 

 i"G. H. Scott, Biol. Symposia 10, 277 (1948). 



