d-aminolevulinic acid synthase:

A. Requires pyridoxal phosphate for activity.
B. Synthesis can be induced by phenobarbital
and some steroids.
C. Is inhibited by heme.
D. 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!

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

This was the last question!