132 alexander l. dounce 



5. Composition with Respect to Enzynes 



The identification of the enzymes in the cell nucleus is a field beset with 

 many pitfalls, and in spite of the considerable amount of work which has 

 been done in several laboratories, many of the published results are of 

 doubtful validity. In general, too many enzymes have been studied and too 

 little effort has been spent in attempting to determine what enzyme trans- 

 locations from the nucleus to the cytoplasm and vice versa are likely to 

 occur during the various isolation procedures. In the opinion of the writer, 

 one of the soundest approaches to the problem of enzyme translocation 

 available at present is to make a comparative study of nuclei isolated by 

 different procedures. The same point of view has been expressed by Beh- 

 rens.^^ 



Certain results concerning the enzyme composition of cell nuclei are 

 nevertheless fairly clear at the present time. In the following paragraphs 

 a complete list of all nuclear enzymes studied thus far will not be given, 

 owing to uncertainties as to the reliability of the work. A fairly complete 

 table of enzymes of cell nuclei can be found in a recent book by Lang,"' 

 and a review of the present status of the enzyme chemistry of isolated cell 

 nuclei has recently been prepared by the writer."'^ Only a rather brief 

 summary of results will be given here. 



a. 0:Qidative Enzymes. In studies on the enzymes cytochrome oxidase and 

 succinic dehydrogenase^'*""* in liver cell nuclei isolated at pH 6.0, it was 

 found that although succinic dehydrogenase could scarcely be detected, 

 cytochrome oxidase was always present at an activity per unit of dry 

 weight of 50 % or more of the corresponding activity for the whole homoge- 

 nate. Schneider and Hogeboom"* found similar results for cytochrome oxi- 

 dase, but argued that the concentration observed was too low to be of sig- 

 nificance. Succinic dehydrogenase was found by them in the same ratio to 

 cytochrome oxidase as in the whole homogenate. The reasoning of Schnei- 

 der and Hogeboom that an enzyme of a cell particulate should not be con- 

 sidered as of significance unless a large proportion could be recovered in the 

 particulate in question, was criticized by Dounce*"* and by Mirsky et alP 

 It was also pointed out'*'*" that the nuclear preparations of Schneider and 

 Hogeboom were contaminated by microscopically visible impurities to such 

 an extent that a resolution of the disagreement could not be obtained by a 

 study of their nuclei. Graffi and Junkman"^ had found in 1946 that nuclei 

 isolated from mouse ascites tumor cells were practically free from cyto- 



"' K. Lang, "Der Intermediare Stoffwechsel." Springer, Berlin, 1952. 



'13" A. L. Bounce, Intern. Rev. Cytol. 3, 199 (1954). 



"* A. L. Bounce, J. Biol. Chem. 147, 685 (1943). 



1'* W. C. Schneider and G. H. Hogeboom, Cancer Research 11, 1 (1951). 



"« A. L. Bounce, Cancer Research 11, 562 (1951). 



'17 G. Graffi and K. Junkman, Klin. Wochschr. 5/6, 78 (1946). 



