Essay on Inhibition of Alcohol Dehydrogenase

671 Words Nov 3rd, 2014 3 Pages
Case 13
Inhibition of Alcohol Dehydrogenase
Focus concept
The inhibition of the alcohol dehydrogenase by a formamide compound is examined.

Prerequisites
C
C

Principles of enzyme kinetics
Identification of inhibition via Lineweaver-Burk plots

Background
Alcohol dehydrogenase (ADH) is the enzyme that is responsible for converting ethanol to acetaldehyde (the reaction is shown in Figure 13.1). It is the enzyme responsible for the metabolism of ethanol in the alcoholic beverages we consume. Five different isozymes of ADH have been identified, and it has been shown that the enzyme has a rather broad substrate specificity and can oxidize aldehydes as well as primary and secondary alcohols. For example,
ADH can also oxidize methanol (wood
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3. The authors of this study studied the ability of N-1,5-dimethylhexylformamide to inhibit mouse
ADH1. The activity of the enzyme was measured in the absence of inhibitor, and in the presence of 1.0 :M inhibitor. The data are presented in Table 13.1.
Table 13.1: Inhibition of mouse ADH1 by N,1-5-dimethylhexylformamide

Ethanol
Concentration, mM

ADH1 velocity, ) NADH absorbance/min (without inhibitor) ADH1 velocity, ) NADH absorbance/min (with inhibitor) 0.20

0.036

0.022

0.25

0.042

0.024

0.36

0.048

0.027

0.60

0.065

0.029

2.00

0.075

0.033
2

a. What are the KM and Vmax values for ADH in the absence of inhibitor? in the presence of the inhibitor?
b. What type of inhibitor is N-1,5-dimethylhexylformamide? Explain.
c. Calculate the values of " and/or "’, if they are significantly different from 1. What kind of inhibitor is N-1,5-dimethylhexylformamide? Explain.
d. Calculate the Ki and/or Ki’ (whichever is appropriate) for N-1,5-dimethylhexylformamide
(Hint: You can obtain these values from " and "’).
4. The authors describe the mechanism of ADH as an “ordered bi-bi” mechanism. Give a written description of the mechanism, as shown in Figure 13.2. How does N-1,5dimethylhexylformamide inhibit the activity of the ADH enzyme? How does N-1,5dimethylhexylformamide differ from the “classic” inhibitors of this type that are described in our textbook?
5. The authors found that a class of compounds called pyrazoles were also inhibitors of
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