74 STUDIES ON ALKALINE PHOSPHATASE 



plasmic side of the membrane, and the other part of the extended 

 protein chain on the environmental side of the membrane. On 

 the environmental side there is a specific adsorbing group which 

 possesses a high affinity for the substance 6. If now A.T.P. comes 

 into contact with the intracellular part of the protein, the protein 

 contracts and folds, as indicated on the lower part of the figure. 

 This contraction retracts the part of the protein chain containing 

 the complex RO from the external surface of the cell into the 

 internal surface. On reaching the internal surface, the folding 

 of the protein becomes such that the affinity of the adsorbing 

 group can be satisfied by internal forces in the coiled protein 

 molecule, so that the group 6 is discharged into the interior of 

 the cell. 



There are a considerable number of possibilities for the details 

 of such a mechanism. The contraction of a protein molecule 

 under the action of A.T.P. is, of course, already well established 

 in the case of the myosin-actin complex. One of the simplest 

 working hypotheses would be that combination of the protein 

 with A.T.P. results in coiling of the protein molecule so as to 

 carry out the transference of 6. If, as is the case with myosin, 

 the protein has phosphatase activity, the A.T.P. will eventually 

 be split and extension of the protein will occur again so that the 

 original configuration of the molecule is restored, and a fresh 

 cycle of transfer of may occur. If the protein is acting as a 

 simple phosphatase, inorganic phosphate will be split off. On the 

 other hand, it may well be that the protein will act as a phos- 

 phokinase, in which case it may not be 6 but the phosphate of 6 

 (i.e., 0OPO3H2) which is split off. It might well be that the 

 process of splitting off a phosphorylated 6 and the extension of 

 the protein are simultaneous. 



A mechanism such as that just suggested would provide a very 

 adequate explanation of the close correlation of alkaline phos- 

 phatase and/or phosphokinase with sites of glucose transfer. 

 That A.T.P. is involved would mean that the process is indirectly 

 linked with respiration and/or glycolysis. 



The mechanism which has been proposed above can be of very 

 general application. The nature of the molecule which is trans- 

 ported would depend almost entirely on the affinity of the adsorb- 

 ing group on the protein. Thus it should not be difficult for such 

 a system, with appropriate variations in the adsorbing group, to 



