Question 13 of 13

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Delta-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.

A. 1, 2 and 3

B. 1 and 3

C. 2 and 4

D. 4 only

E. All of the above

The correct answer is (A).

Comments:

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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Last modified 1/5/95