Melonate inhibits the growth of pathogenic bacteria by inhibiting the activity of

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Question

Melonate inhibits the growth of pathogenic bacteria by inhibiting the activity of

Accepted Answer

Correct Answer: D — Succinic dehydrogenaseStep-by-step Solution:Malonate (melonate) is a dicarboxylic acid (HOOCCH₂COOH) that is a structural analogue of succinate (HOOCCH₂CH₂COOH). Succinate dehydrogenase (SDH, Complex II of the electron transport chain) catalyses the oxidation of succinate to fumarate in the TCA cycle: Succinate + FAD → Fumarate + FADH₂. Malonate, because of its close structural similarity to succinate, competitively inhibits succinate dehydrogenase by competing for the enzyme's active site without being oxidised. This blocks the TCA cycle and the electron transport chain, thereby disrupting energy production (ATP synthesis) in bacteria and inhibiting their growth. The inhibition is reversible and competitive — it can be overcome by increasing the concentration of the substrate succinate. This is a classic example of competitive inhibition used in biochemistry studies.Why other options are incorrect: Amylase (A) hydrolyses starch to maltose — malonate has no structural resemblance to starch substrates and does not inhibit amylase. Lipase (B) hydrolyses triglycerides — malonate is not structurally related and does not inhibit lipase. Dinitrogenase (C) is the enzyme component of nitrogenase complex involved in nitrogen fixation — it contains molybdenum-iron cofactor; malonate does not inhibit it.Key Concepts:Competitive inhibition: Inhibitor resembles the substrate structurally; competes for active site; increases apparent Km without changing Vmax; reversible by excess substrate.Malonate vs succinate: Classic example of competitive inhibition (Km increases, Vmax unchanged).Succinate dehydrogenase (SDH = Complex II): TCA cycle enzyme; located on inner mitochondrial membrane; links TCA cycle to ETC via FADH₂.Other competitive inhibitors: methanol inhibits alcohol dehydrogenase (same active site as ethanol); sulfanilamide inhibits bacterial dihydropteroate synthase (PABA analogue).

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