68 STUDIES ON ALKALINE PHOSPHATASE 



nucleolar activity is associated with protein synthesis, and, as 

 we have noted before, nucleoli are usually one of the most phos- 

 phatase-rich regions of a cell. On the other hand, it is not pos- 

 sible to maintain that there is a direct correlation between the 

 cytochemically demonstrable alkaline phosphatase and protein 

 synthesis in all cases. Thus, though some tumours are rich in 

 alkaline phosphatase, other tumours which are growing equally 

 rapidly, such as the Rous chicken carcinoma, contain relatively 

 little phosphatase. We must also recall that the formation of 

 skin keratin and of the byssus thread of Mytilus do not appear 

 to be associated with alkaline phosphatase. It is, of course, pos- 

 sible that there are amounts of alkaline phosphatase in the cells 

 carrying out syntheses of these last two proteins which are suffi- 

 cient for the purposes of the cell but which are too small to be 

 demonstrated cytochemically. Alternatively, it may be that 

 with certain proteins the function performed by alkaline phos- 

 phatase is taken over by a more labile phosphatase. Whatever 

 the explanation may be of the fact that presence of alkaline 

 phosphatase cannot always be demonstrated in connection with 

 protein synthesis, the fact remains that there is a very close cor- 

 relation of occurrence of alkaline phosphatase with protein syn- 

 thesis and with certain stages in differentiation. As Dale has 

 said in connection with the correlation between liberation of 

 acetylcholine at motor end plates and muscular contraction, it 

 can hardly be that the correlation exists simply to mislead in- 

 vestigators ! Further work, however, is essential in this field. As 

 we shall see towards the end of this chapter, it is conceivable 

 that the alkaline phosphatase is connected, not with synthesis 

 of proteins, but with their activities immediately after synthesis. 

 It may well be that studies on Protozoa along lines similar to 

 those of Mugard will yield vital information. 



Alkaline Phosphatase and Secretion 



Verzar (1936) suggested that the process of secretion of sub- 

 stances across cell membranes might be connected with phos- 

 phorylation. Wilbrandt obtained some evidence for this by the 

 use of enzyme poisons to inhibit secretion. His results have been 

 confirmed by numerous other workers. It has also been shown 



