PHOSPHATASE AND DIFFERENTIATION 67 



cell should store phosphate, and that the phosphate ester should 

 then be released in a wave over a brief period. It seems equally- 

 probable, so far as the evidence at present available is concerned, 

 that the glycogen is not directly concerned in calcification. In- 

 deed, it may even be that hydrolysis of phosphate esters (derived 

 ultimately from the blood stream) in the cartilage raises the 

 concentration of glycogen precursors to such an extent as to 

 cause glycogen formation in cartilage cells as an indirect effect 

 of calcification, i.e., that the phosphate moiety of the phosphate 

 esters is being deposited as calcium phosphate in the cartilage 

 while the other moiety of the molecule is being deposited as glyco- 

 gen in the cartilage cells. 



Alkaline Phosphatase and Differentiation 



From the data which have been presented above there have 

 been a number of hints that alkaline phosphatase may be con- 

 cerned in certain steps at any rate in the process of differentia- 

 tion. We know so little of the mechanism of differentiation that 

 it is difficult to formulate a detailed suggestion as to how such 

 an enzyme may be participating. The difficulty is enhanced by 

 the fact that the same enzyme appears to operate both as a hy- 

 drolytic enzyme and as a phosphokinase. But, although it is 

 not possible at the present time to produce a detailed physico- 

 chemical working hypothesis for the function of alkaline phos- 

 phatase in connection with differentiation, there is an impressive 

 body of evidence that there is such a connection. Moog (1944) 

 has shown that in the development of the chick there are waves 

 of formation of alkaline phosphatase at different stages in the 

 development of at least most tissues. Lorch (1949) has recorded 

 a similar finding in the development of dogfish and trout. 

 Yao (1950) has made a similar observation with Drosophila 

 larvae. Runnstrom and his colleagues have also shown that 

 there is a great increase in alkaline phosphatase concentration in 

 echinoderm eggs immediately after gastrulation. This last ob- 

 servation is particularly striking in that it is not until after 

 gastrulation occurs that a significant quantity of new antigens 

 are formed in the development of the echinoderm larvae. It is 

 at the same stage that nucleoli become prominent in the cells of 

 the developing larvae: Caspersson and his colleagues have pro- 

 duced a good deal of evidence to show that prominence of 



