APPENDIX I: TERMINOLOGICAL CONSIDERATIONS 



The fifth case we can classify as a transport, provided, of 

 course, that we are considering the process as a whole, as a mode 

 of inorganic phosphate entry into the cell. In this transport a phos- 

 phoryl translocation, for example as visualized in Figure 17, may 

 prove to be the decisive step, although only a step. The fact that 

 we may know the intermediates in this hypothetical case naturally 

 does not move the case out of the area of transport. 



The term active transport 



At one time an effort was made to reserve the term transport 

 for movements against concentration gradients, the term transfer 

 being suitable for movements in any direction (cf. Maizels, 1954). 

 Obviously, this distinction has now been lost. One can only deplore 

 any tendency now to empty of meaning the qualifying adjective 

 in the term active transport. 



The only generally accepted criterion is that the transport be 

 able to operate against a concentration gradient (Rosenberg, 1954), 

 or that the flux ratio depart from the concentration ratio between 

 the two phases (Ussing, 1949). 



Perhaps the adjective active has seemed to give a superior stand- 

 ing to a transport so that the temptation to use it without meeting 

 either form of this criterion has been great. The demonstration of 

 a high temperature coefficient is not adequate, nor is a dependence 

 on energy-yielding metabolism convincing, since a steady supply 

 of metabolic energy may serve only to maintain the supply of a 

 transporting or a binding structure. As a further caution, note that 

 dinitrophenol accelerates a mediated entrance of glucose into mus- 

 cle, but inhibits its uphill transport into kidney slices. Furthermore, 

 one can expect for many solutes that they may be bound to cellular 

 components, so that a demonstration that a cell accumulates a given 

 substance does not prove that an active transport (or indeed any 

 transport) has taken place. 



The term permease 



In 1957 Cohen and Alonod wrote: 



Thus the role of permeases as chemical connecting links be- 

 tween the external world and the intracellular metabolic world 

 appears to be decisive. . . . Moreover, since the pattern of inter- 



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