In Corynebacterium glutamicum, tryptophan biosynthesis is primarily regulated at which enzymatic step(s)?

Introduction / Context:
Tryptophan biosynthesis branches from the shikimate pathway. Regulation typically occurs at the entry to the aromatic pathway and at the first committed step toward tryptophan. The organism Corynebacterium glutamicum is a major industrial microbe; understanding its control points is key for amino acid overproduction strategies.

Given Data / Assumptions:

• DAHP synthetase catalyzes condensation of erythrose-4-phosphate and phosphoenolpyruvate to yield DAHP, the entry to the aromatic pathway.
• Anthranilate synthase commits flux toward tryptophan by converting chorismate to anthranilate.
• Feedback inhibition by aromatic amino acids modulates these steps.

Concept / Approach:
Control of tryptophan biosynthesis is distributed: DAHP synthetase balances overall aromatic flux and is feedback-controlled by end products; anthranilate synthase is often specifically inhibited by tryptophan. Engineering for higher tryptophan titers therefore targets both enzymes: desensitizing feedback at DAHP synthetase to increase total aromatic flow and relieving inhibition at anthranilate synthase to channel more chorismate to tryptophan.

Step-by-Step Solution:
Identify the entry-point enzyme (DAHP synthetase) controlling total aromatic carbon flow.Identify the branch-point enzyme (anthranilate synthase) committing to tryptophan.Note feedback inhibition patterns relevant to C. glutamicum.Conclude that regulation operates at both steps.

Verification / Alternative check:
Metabolic engineering literature repeatedly reports improved tryptophan titers by mutating/desensitizing both DAHP synthetase and anthranilate synthase in Corynebacterium spp.

Why Other Options Are Wrong:
DAHP synthetase only: misses the specific branch control by anthranilate synthase.Anthranilate synthase only: ignores upstream flux limitation at DAHP formation.Phosphoenolpyruvate: a metabolite, not the regulatory enzyme per se.

Common Pitfalls:
Tuning only one node and neglecting the upstream carbon supply into the aromatic pathway.

Final Answer:
Both (a) and (b)