Cycloserine, a second-line anti-TB drug, inhibits cell wall synthesis by targeting which two sequential enzymes?

• A D-alanyl-D-alanine synthetase and transpeptidase
• B Alanine racemase and UDP-galactopyranose mutase
• C D-alanine racemase and D-alanyl-D-alanine synthetase ✓
• D UDP-N-acetylmuramate synthetase and D-glutamate ligase

Explanation

Cycloserine (a D-alanine analogue) inhibits two enzymes in the cytosolic steps of peptidoglycan synthesis: alanine racemase (converts L-alanine to D-alanine) and D-alanyl-D-alanine synthetase (joins two D-alanine molecules). This prevents formation of the pentapeptide precursor. CNS toxicity (seizures, psychosis) occurs because cycloserine also acts as a GABA analogue and crosses the blood-brain barrier; pyridoxine supplementation is recommended.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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