BIOLOGICAL TRANSPORT 



Wilbrandt and Rosenberg (1961) supplied a kinetic equation 

 for the competition of such an inhibitor with the substrate for 

 combination with the carrier, specifically for an inhibitor that 

 reaches the same concentration on the two sides of the membrane: 



/ Sj #2 \ 



Fmax \S{ +/' + 1 " £ 2 + /' + 1/ 



(9) 



5' and /' are the relative concentrations of the solute and the in- 

 hibitor, with reference to the relevant value of K m : 



S I 



S' = and V = — 



For application to uphill transport, different values of K m should 

 presumably be used for each of the two directions of flux. These 

 authors show that this equation requires that the inhibitor will not 

 only inhibit at higher levels, but that it will also accelerate transport 

 by driving exchange at relatively low levels in the manner shown 

 earlier by Heinz and Walsh (1958). A sequence of initial inhibition 

 followed by acceleration can arise in the more complex but practi- 

 cal situation where the inhibitor is initially placed in one phase 

 only, and then is itself concentrated into the other phase. Experi- 

 ments, to be described in the next chapter, indicate that K x /K 2 

 may be very different for different amino acids, i.e., that one amino 

 acid may lose much more apparent affinity than another through 

 carrier modification, complicating the problem still further, whether 

 the net effect will be an inhibition or stimulation of uptake. 



In this connection, Jacquez (1961) has introduced the use of a 

 computer to test the kinetic requirements of various models for 

 amino acid transport. 



5 2 



