PHOSPHATASES OF NUCLEI OF OTHER CELLS 55 



Figure B of Plate VI shows such a section. The dye material 

 appears only in the nuclei of the cells. As in this experiment the 

 brush-border enzyme was inert, it follows that the nuclear enzyme 

 is intrinsic in the nuclei. 



In obtaining such distinction in activity between nuclear and 

 brush-border phosphatases, we were, of course, fortunate to a 

 degree which we cannot expect to see repeated with other tissues. 

 We have also obtained evidence, by destroying enzymes by heat, 

 that nuclear phosphatase is less readily destroyed than is brush- 

 border phosphatase of rat kidney. There thus appear to be two 

 differences between the alkaline phosphatases in rat-kidney nuclei 

 and rat-kidney brush borders. It does not, however, necessarily 

 follow that the enzymes in these two sites are different. It may 

 be that the enzymes in these two sites are adsorbed upon different 

 materials: this might just possibly be sufficient to account for 

 the difference in behaviour. 



The Phosphatases of the Nuclei of Other Cells 



The work mentioned above dealt only with the alkaline phos- 

 phatase of the brush-border cells of the proximal tubules of mam- 

 malian kidney. In the papers of Takamatsu and Gomori pub- 

 lished in 1939 it was mentioned that phosphase is rather com- 

 monly demonstrated in a variety of nuclei. Willmer and Krugelis 

 independently showed in 1942, in a study of tissue cultures, 

 that in mitosis the greater part of the nuclear phosphatase be- 

 comes concentrated on the chromosomes. From these results 

 it was evident that phosphatase might be playing an important 

 role in some of the chemical activities of the nucleus. 



The tendency for phosphatase to become concentrated on the 

 chromosomes during cell division seems to be a fairly common 

 phenomenon. It may be noted, for example, in regenerating 

 liver cells, in tumor cells, and in various embryonic tissues. 

 Plate VII, Fig. A, shows phosphatase present in a normal rat 

 liver. The main sites of activity in the nucleolus and the chro- 

 mocentres are clearly demonstrated. Figure B in the same 

 plate shows that when a liver is regenerating, the nuclear phos- 

 phatase is concentrated on the chromosomes during the nuclear- 

 division phase. This type of behaviour, i.e., the presence of alka- 

 line phosphatase on chromosomes, nucleoli, and chromocentres, 

 is not limited to mammalian tissues. It has been found in am- 



