76 STUDIES ON ALKALINE PHOSPHATASE 



nucleus the richest sites of phosphatase are the chromocentres 

 and particularly the nucleoli: in Drosophila salivary chromo- 

 somes the Feulgen-positive bands contain most of the nuclear 

 phosphatase. It is probable that in the living cell all these re- 

 gions are either in a steadily contracted state, or in a state of 

 intermittent contraction. This latter suggestion has many points 

 of interest. There is no reason to believe that intermitotic 

 chromosomes are inert except so far as purely chemical processes 

 are concerned. Contractility in active regions of chromosomes 

 might well play a significant part in the shedding of gene prod- 

 ucts, or in effecting the folding of synthesized polypeptide chains 

 into globular proteins. 



2. The association of phosphatase with newly formed collagen, 

 first discovered by H. B. Fell, has evoked many speculations as 

 to its significance. To my view, none of these speculations have 

 acted as a beacon by which a path for further advance could be 

 plotted. But, if the significance of the association is that new 

 collagen is a contractile protein, a new way does become clear. 

 One of the most dramatic phenomena in the healing of a wound 

 is the contraction which occurs as new collagen is laid down. 

 This contraction occurs at the time at which the collagen is rich 

 in phosphatase. In vitamin C deficiency, although much fibrous 

 protein is formed in a healing wound, no phosphatase is found, 

 and no contraction occurs. If newly formed connective-tissue 

 protein is normally contractile, we may indeed expect the con- 

 tractility to be of marked physiological importance. For ex- 

 ample, in organizing the structure of bone, collagen contractility 

 may be involved. 



3. Although alkaline phosphatase has been observed to be 

 associated with the centrosome and spindles, it has not yet been 

 demonstrated by critical studies that this represents intrinsic 

 phosphatase. But if there is in fact phosphatase in these posi- 

 tions in the living cell, we should again be provided with a new 

 route of inquiry into the nature of spindle action. 



Thus it may be seen that, although the cytochemical study of 

 enzymes is at present conducted on a relatively crude basis, it 

 bears many signs of being a skeleton key which will open many 

 of Nature's locks. With increasingly critical usage, we are likely 

 to find in such studies a far more delicate weapon than are the 

 common methods of biochemistry. 



