Question 16 of 16

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Allopurinol is an inhibitor of xanthine oxidase. Administration of allopurinol to a patient with gout and normal HG-PRT levels would be expected to lead to all of the following EXCEPT:

A. decreased de novo synthesis of IMP.

B. decreased urate in the urine.

C. an increase of hypoxanthine in the blood./a>

D. increased levels of PRPP .

E. tincreased xanthine in the blood.

Comments:

A. As long as HG-PRT is available, the increased xanthine and hypoxanthine will be salvaged to GMP and IMP, both of which inhibit the rate limiting step of the synthesis..

B. Allopurinol directly inhibits the production of urate.

C. Hypoxanthine is a substrate for the inhibited enzyme and, therefore, increases.

D. As long as HG-PRT is available, the increasing xanthine and hypoxanthine will consume PRPP. Contrast this to the situation with the Lesch-Nyhan syndrome.

E. Xanthine is a substrate for the inhibited enzyme.

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Last modified 1/5/95