INTRODUCTION AND THEORETICAL CONSIDERATIONS 455 



alter the internal concentration of the factor, while concentrations of 

 the externally supplemented substrate higher than that synthesized by the 

 system would attain an equilibrium with the concentration within the 

 system. Since the amount of substrate synthesized would merely be addi- 

 tive to total external and internal concentrations, the total external and 

 resulting internal concentration would not be materially affected by such 

 synthesis in many systems, e.g., inhibition of growth of a small inoculum 

 in bacterial growth medium. 



On the other hand, the transition may be gradual in some systems, e.g., 

 embryonated eggs, in which the amount of substrate synthesized or 

 initially present is appreciable in comparison with the total amount of 

 substrate supplied. The transition indicated in Figure 2 is minimized 

 to indicate the intermediate effect between two possible extremes. 



These effects have not seriously limited the application of this method 

 in determining the type of inhibition in certain biological systems, but 

 may have altered some of the quantitative aspects of data derived by the 

 method. 



This method was applied by Wyss 19 to the effect of p-aminobenzoic 

 acid on the growth inhibition of Escherichia coli resulting from the action 

 of sulfanilamide. The results indicate that sulfanilamide competitively 

 inhibits the functioning of p-aminobenzoic acid. The rate of growth of 

 the organism inhibited by sulfanilamide was considered to be proportional 

 to the rate of the inhibited enzymatic reaction, and the total enzyme 

 concentration of the bacterial cell was assumed to be constant, since 

 mother and daughter cells have the same enzyme concentration. Essen- 

 tially, it is assumed that no resistance to sulfonamide develops under the 

 testing conditions. Although some resistance may develop during the 

 determination of growth rate, it does not seriously affect the qualitative 

 results, but may affect conclusions which are based on quantitative cal- 

 culation. This method has also been applied to the reversal by p-amino- 

 benzoic acid of the toxicity of other sulfonamides for Escherichia coli. 20 



By a method similar to that used in the derivation of the above rate 

 equations, an expression can be derived for the competitive inhibition of 

 the combination of a coenzyme with an apoenzyme. Thus 



where the symbols are identical with those previously indicated. In the 

 graphical presentation of the data with 1/r plotted against l/[Co], the 

 intercept of 1/r at l/[Co]=0 does not change with changes in inhibitor 

 concentration, but the slope of the linear relationship increases with 

 increasing concentrations of inhibitor. 



