SUGGESTIONS FOR PLOTTING AND DETEEMINATION 191 



(2) Utilize all the intercepts and intersections available in the plots 

 because accuracy in the determination of constants is increased and the 

 calculation often made more direct. For example, Dixon (1953 b) showed 

 that K^ may be immediately calculated from the intersection of lines in 

 the plot of \jv^ against (I) for competitive inhibition, which may be more 

 accurate than determinations from the slope or (I) intercept. 



(3) It is obvious from what has been said above that consideration be 

 given to the other components of the enzyme system with respect to the 

 effects they have on the slopes and intercepts; in other words it is impor- 

 tant to calculate the true K^ and not a physically meaningless constant 

 which at best only characterizes the behavior of the inhibition. 



(4) Consider all of the possible mechanisms which may be implied by 

 the curves obtained. It is frequently easy to decide upon a mechanism as 

 a matter of simplicity or prejudice without realizing that the data could 

 equally well indicate other mechanisms. It is usually possible to eliminate 

 most of the suggested mechanisms if it is realized that there are several 

 possibilities. 



(5) Although problems of inhibition in tissues, cells, and subcellular 

 fractions have not been discussed, it is well to point out that special care 

 must be exercised in the interpretation of plots made from data on such 

 systems. Particularly when the measurements involve responses to enzyme 

 inhibition that are far removed from the enzyme, one should put little re- 

 liance on the techniques of plotting devised for relatively simple systems. 

 Permeability factors alone may distort the basic inhibition kinetics beyond 

 ready interpretation. 



The following list of papers and works on kinetics and the plotting of 

 enzyme reactions, both uninhibited and inhibited, is recommended for 

 further refence: Lineweaver and Burk (1934), Hunter and Downs (1945), 

 Wilson (1949, p. 16), Dixon (1953b), Friedenwald and Maengwyn-Davies 

 (1954, pp. 154, 180), Slater (1955), Alberty (1956b), Hofstee (1956), Dixon 

 and Webb (1958), Neilands and Stumpf (1958), Laidler (1958), Hearon 

 et al. (1959, p. 49), and Reiner (1959). 



