Drug Metabolism in Drug Design and Development Basic Concepts and Practice

V/S

(ml/min/mg protein)

0.05

0.10

0.15

0.20

(^403020) (nmol/min/mg protein)V 10 0

S

(μM)

0

200

400

600

800

1000

(nmol/min/mg protein)V
40 30 20 10 0

(a)

(b)

1/S

(1/μM)

-0.02 0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.6 0.5 0.4 0.3 0.2 (1/nmol/min/mg protein)0.11/V 0.0 -0.1

(c)

FIGURE 13.2

Biochemical plots for the enzyme kinetic characterizations of biotransformation. (

a) Direct concentration-rate or Michaelis–

Menten plot; (

b), Eadie–Hofstee plot; (

c), double-reciprocal or Lineweaver–Burk plot. The Michaelis–Menten plot (

a), typically exhibiting

hyperbolic saturation, is fundamental to the demonstration of the effects of substrate concentration on the rates of metabolism, or metaboliteformation. Here, the rates at 1 mM were excluded for the parameter estimation because of the potential for substrate inhibition. Eadie–Hofstee (

b) and Lineweaver–Burk (

c) plots are frequently used to analyze kinetic data. Eadie–Hofstee plots are preferred for determining the

apparent values of

K

m

and

Vmax

. The data points in Lineweaver–Burk plots tend to be unevenly distributed and thus potentially lead to

unreliable reciprocals of lower metabolic rates (1/

V); these lower rates, however, dictate the linear regression curves. In contrast, the data

points in Eadie–Hofstee plot are usually homogeneously distributed, and thus tend to be more accurate.

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