The broad-spectrum herbicide glyphosate, the active ingredient of Roundup, inhibits this enzyme
The broad-spectrum herbicide glyphosate, the active ingredient of Roundup, inhibits this enzyme
Select an option to attempt
Correct Answer: Option D
Explanation
Glyphosate (N-phosphonomethylglycine) is the active ingredient of Roundup® herbicide (Monsanto/Bayer). Target: EPSPS (5-enolpyruvylshikimate-3-phosphate synthase), EC 2.5.1.19, the penultimate enzyme in the shikimate pathway. EPSPS catalyses: Shikimate-3-phosphate + PEP (phosphoenolpyruvate) → 5-EPSP +. Glyphosate is a competitive inhibitor with respect to PEP — it binds in the PEP-binding site of EPSPS in the presence of shikimate-3-phosphate, forming a stable ternary complex. The shikimate pathway is essential in plants (and bacteria, fungi) for synthesising chorismate → phenylalanine, tyrosine, tryptophan (aromatic amino acids) + folate. Animals lack the shikimate pathway — they obtain aromatic amino acids from diet — explaining glyphosate's low acute toxicity to mammals. Glyphosate-resistant crops carry CP4-EPSPS from Agrobacterium (has low glyphosate affinity).