STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 75 



while a great many are concentrated in mitochondria. Some enzymes, such 

 as ATPase or nucleoside phosphorylase, appear to be distributed in many 

 fractions. However, the apparently wide distribution of uxicase arises in the 

 difficulties of cleanly separating the lysosomes within the mitochondrial 

 fraction. As wiU be noted below, many enzymes are also found in the cell 

 sap, e.g., glycolytic system, various dehydrogenases. 



It is important to stress that these distributions are given for rat liver 

 and that other distributions may be fomid for other tissues of the same 

 animals or for other cells. For example, hippurate synthesis, centered in 

 mitochondria of rat liver, is not found in mitochondria of heart (Green, 1954). 

 The oxidative hexosemonophosphate pathway, found in large part in cell 

 sap, nevertheless appears to be organized in rather tiny particulates in rabbit 

 liver (Newbujgh and Cheldelin, 1956). Also, Green (1957) refers to work of 

 Gale to the effect that the entire glycolytic system of Staphylococcus is 

 associated with the protoplast membrane of the bacterium rather than in the 

 soluble state foimd in liver nuclei or cell sap. 



Knowledge of these distributions should be of great value in following the 

 course of virus purification. It should be known if a virus such as influenza 

 virus carries some of these enzymes in addition to antigens characteristic of 

 the host. Sharp et al. (1954) have described the association of ATPase with 

 the virus of avian myeloblastic leukosis. Does this ATPase normally exist 

 in a cellular component of comparable size? Do other enzymes exist on such 

 a component? Are they also associated with the virus? Studies of this type 

 have not yet appeared. Such information would also be of considerable 

 relevance to the problems of viral origin. 



C. Enzymatic Systems of Nuclei 



Table VIII A reveals that known enzymes concentrated in isolated nuclei 

 include a group of systems capable of degrading intermediates of nucleic 

 acid metabolism, and arginase, which converts arginine to ornithine and 

 urea. These substrates are known to be present m nuclei. Although it has 

 been suggested (Allfrey et al., 1955b) that the relatively high concentration 

 of nucleoside phosphorylase (as well as adenosine deaminase and guanase) 

 reflect an accumulation of enzymes concerned with nucleic acid synthesis, 

 the nature of these enzymes are not such as to suggest a synthetic role rather 

 than a degradative one. Some workers have found these enzymes in a soluble 

 fraction rather than in nuclei (Schneider and Hogeboom, 1956). 



The extraordinary concentration of the system synthesizing DPN (DPN 

 pyrophosphorylase) in this organelle should be noted; according to Hogeboom 

 and Schneider (1952) the enzyme is present only in nuclei. The reaction 

 catalyzed by this enzyme is: 



