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


  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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