PHOSPHATASE AND DIFFERENTIATION 63 



centres, and the chromosomes found during mitosis are strongly 

 positive. 



Dr. Mugard inclines to the view expressed by Brachet, that al- 

 kaline phosphatase is related to the rate of deoxy nucleic acid 

 turnover. It is, however, difficult to reconcile this view with the 

 fact that alkaline phosphatase remains constant in amount in 

 the sea-urchin egg until gastrulation occurs, whereas a consider- 

 able synthesis of deoxy nucleic acid occurs before gastrulation. 



A more extended study of the relationships among nucleic acids, 

 proteins, and alkaline phosphatases in Protozoa is required. The 

 situation is becoming somewhat complicated by the fact that it 

 appears unlikely that there is only one alkaline phosphatase. I 

 have found that there is often a difference in properties between 

 nuclear and cytoplasm phosphatase. Ross and Ely (1951) have 

 recently made the very much more striking observation that there 

 is a high tendency for substrate specificity with some nuclei. For 

 example, with Habrabracon the nucleus contained no enzyme cap- 

 able of reacting with glycerophosphate or with adenosine phos- 

 phate. On the other hand, adenosine diphosphate and triphos- 

 phate are both rapidly attacked by nuclear enzymes. They have 

 also found that, in plant tissues where there is an apparent ab- 

 sence of glycerophosphatase (possibly due to hypersensitivity to 

 fixatives), there is a vigorous reaction with certain nucleotides 

 and not with others. So far as the evidence goes at the moment, 

 we must contemplate the possibility that there may be many al- 

 kaline phosphates, which may be individually concerned with 

 either nucleic acid or protein synthesis, or with both. 



Alkaline Phosphatase, Protein Synthesis, and 



Differentiation 



Formation of Fibrous Proteins. 



Fell and Danielli (1943) made a study of the action of some 

 chemical warfare agents upon rat skin. In the course of this 

 work, Miss Fell observed that at the site of a small healing skin 

 lesion there was a very strong phosphatase reaction. A study 

 was therefore made of the distribution of alkaline phosphatase 

 in healing wounds. We observed that phosphatase occurred to a 

 considerable concentration in proliferating cells, and that as new 



