2. Ethanol and methanol are both substrates for alcohol dehydrogenase (ADH). In

Question

2. Ethanol and methanol are both substrates for alcohol dehydrogenase (ADH). In times of methanol poisoning, ethanol is given as treatment to prevent ADH from converting methanol to the dangerous by-product formaldehyde (which by the way is the major component in embalming fluid to preserve cadavers). a. Consider the Km values for each of these substrates with enzyme ADH. Discuss Km values for ADH with each substrate and compare their magnitude? WHY? BE CLEAR AND CONCISE. b. Is methanol truly an inhibitor of the enzyme ADH? Why or why not?

Explanation / Answer

Ans 2a)

Km (ethanol) = 2.1 x 10-2 M

Km (methanol = 1.3 x 10-1 M

Km is a measure of the substrate concentration required for effective catalysis to occur. So, a high Km simply means that a higher concentration of substrate is required to achieve a particular reaction velocity in comparison to a substrate with a low Km. Ethanol in this case have a low Km in comparison to methanol.

Ans 2b) Methanol is per se not inhibitor of enzyme ADH but it competes with ethanol for the active site. Hence, methanol toxicity is treated with higher doses of ethanol. What ethanol does is that it replaces methanol in the active site by competiting with methanol. Since, methanol have high Km and have low concentration, ethanol binds to ADH's active site thus prevents methanol toxicity.

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