d-aminolevulinic acid synthase:

1. Requires pyridoxal phosphate for activity.
2. Synthesis can be induced by phenobarbital and some steroids.
3. Is inhibited by heme.
4. Is inhibited by lead.

1. A, B and C
2. A and C
3. B and D
4. D only
5. All of the above

Right

1. Pyridoxal (vitamin B6) phosphate antagonists, such as the anti-tuberculosis drug, isoniazide, can inhibit this enzyme.
2. Phenobarbital is contraindicated for patients with porphyria for this reason.
3. This is a major physiological control.
4. ALA dehydratase and ferrochelatase are notably lead-sensitive.

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