ISOLATION AND COMPOSITION OF NUCLEI AND NUCLEOLI 139 



activity in nuclei isolated by an improved method from normal rat liver. 

 Nuclei of regenerating liver and normal spleen showed somewhat higher 

 catheptic activity, amounting approximately to one-third of the specific 

 activity of whole tissue in the case of spleen. 



c. Enzymes of General Distribution in Tissues Contrasted with Enzymes 

 Peculiar to a Particular Tissue. One of the aims in research on enzymes of 

 cell nuclei is to find out if possible whether cell nuclei are alike or different 

 with respect to their enzyme systems and, if they differ, whether any re- 

 lationship can be found between nuclear and cytoplasmic enzymes or 

 whether there are some enzymes common to all nuclei. 



The writer very early attempted to find a relationship between the en- 

 zymes of cell nuclei and the enzymes commonly found in tumor or growing 

 tissue" but was unable to do so. The work with arginase for example* 

 showed that nuclei can be very diverse in regard to the enzymes which they 

 contain. More recently, Mirsky et al}^ have attempted to analyze the prob- 

 lem relative to particular tissues. According to Mirsky, nuclei differ among 

 themselves as much as do the whole tissues, with respect to enzymes 

 characteristic of particular tissues. Arginase, for instance, was in high con- 

 centration in mammalian liver cell nuclei and calf kidney nuclei relative 

 to the concentration in whole tissue, but it was almost absent from nuclei 

 of fowl kidney. Catalase was present in high concentration in mammalian 

 liver cell nuclei but was absent from fowl and calf kidney nuclei. (In this 

 laboratory catalase was found in relatively high concentration in lamb 

 kidney nuclei isolated in dilute citric acid at pH 6.*") Myoglobin was not 

 present in muscle nuclei, but hemoglobin was present in chicken erythro- 

 cyte nuclei. There was no tendency toward a high nuclear concentration of 

 lipase, amylase, uricase, adenosinetriphosphatase, or alkaline phosphatase 

 in the tissues studied, and in many cases the nuclear concentrations of these 

 enzyme were particularly low. 



Of enzymes of more general distribution, adenylic deaminase and nucleo- 

 side phosphorylase were always in very high concentration in the nuclei 

 studied; esterase was often abundant; but /3-glucuronidase tended to be low. 



Thus no particularly simple generalizations can be derived from the 

 work of Mirsky et alP concerning nuclear enzymes. The subject is dealt 

 with in greater detail in a recent review"^^ and a considerably less positive 

 attitude towards the situation than is adopted by Mirsky may be neces- 

 sary until further results are forthcoming. Certain evidence concerning the 

 permeability of the nuclear membrane brings up the possibility that the 

 latter may be permeable by diffusion to many enzymes, but this point of 

 view is not accepted by Mirsky. 



Hogeboom and Schneider'' have recently reported that most of a DPN- 

 synthesizing enzyme of liver cell nuclei is recoverable in nuclei isolated in 

 sucrose solution by their latest procedure, in spite of the fact that this 



