60 STUDIES ON ALKALINE PHOSPHATASE 



cultures. Figures A to D of Plate XI show the distribution of 

 alkaline phosphatase obtained by the method of Takamatsu 

 and Gomori with chick osteoblast cultures. This work on tis- 

 sue-culture material shows a high concentration of phosphatase 

 in the nuclei. In the intermitotic nuclei by far the highest con- 

 centration of phosphatase is found in the nucleolus: the chromo- 

 centres are also positive for phosphatase. In early prophase the 

 greater part of the chromosome is positive for phosphatase, even 

 before the nucleoli have disappeared. When the nuclear mem- 

 brane breaks down and the spindle is formed, the chromosomes 

 retain practically the whole of the alkaline phosphatase activity 

 of the nuclei, but some activity appears on the spindles and par- 

 ticularly on the centrosomes of the spindles. The cytoplasm also 

 commonly shows a certain amount of phosphatase which appears 

 to be present in rather large cytoplasmic granules. 



The pictures observed with tissue cultures are often so clear- 

 cut that it is tempting to take them at their face value. But it 

 has not so far been possible to study the extent to which the 

 results are complicated by diffusion artefacts. It is clear that 

 the highest centres of phosphatase activity in the tissue cultures, 

 namely, the nucleoli of intermitotic cells and the chromosomes 

 of mitotic cells, have a high intrinsic phosphatase activity. But 

 whether the phosphatase of the chromocentres, of the spindles, 

 and of the cytoplasmic granules is intrinsic or is in part or wholly 

 due to diffusion artefacts is at present in doubt. 



It would, of course, be of the greatest interest if it could be 

 established that there is indeed alkaline phosphatase present in 

 the spindles and in the centrosomes. In sectioned material it is 

 usually not possible to demonstrate alkaline phosphatase in these 

 sites, but I have occasionally found it on the spindle and cen- 

 trosomes in rat tumor tissues. Further investigation of this prob- 

 lem will be of great interest. 



Possible Functions of Nuclear Phosphatase 



Until recently alkaline phosphatase was thought of as an 

 enzyme which was apparently hydrolytic in function, producing 

 phosphoric acid and alcohol from a phosphate ester. Axelrod and 

 MeyerhofT and Green have independently demonstrated in the 

 last few years that phosphatases may also act as phosphokinases, 

 i.e., they may catalyze the transfer of a phosphate residue from 



