70 



STUDIES ON ALKALINE PHOSPHATASE 



adjacent to the tissue spaces, and an equivalent concentration of 

 glucose phosphate against the membrane adjacent to the lumen 

 of the tubules. As glucose penetrates the cell wall much more 

 rapidly than glucose phosphate, there will be a net transfer of 

 glucose across the cell, and thus transfer of glucose from tubules 



Fig. 3. The upper part of the figure shows the distribution of enzyme 



systems required to provide a secretory effect. The lower part of the 



figure shows the concentrations that will arise in the various parts of the 



system as a result of the enzyme actions. 



to tissue spaces may be effected, even against a concentration 

 gradient. 



The mechanism detailed above considers only the secretion of 

 glucose by kidney; in principle, of course, it can be extended to 

 cover the secretion of almost any type of molecule. 



The techniques for the study of alkaline phosphatase have 

 made it possible to see to what extent this enzyme was present in 

 the sites required by the working hypothesis indicated above. 

 Gomori and Takamatsu showed that alkaline phosphatase occurs 

 in the brush borders of the glucose-secreting kidney tubule cells 

 in a variety of mammals. This has also been found to be the 



