Metabolism USMLE Step 1 Practice Question
The enzyme hypoxanthine guanine phosphoribosyl transferase (HGPRT) isolated from a child with Lesch-Nyhan syndrome is compared with HGPRT isolated from a healthy control individual. The results are shown in the graph below (Lineweaver-Burk plot showing Lesch-Nyhan patient HGPRT has higher Km than control). Which of the following is the best conclusion about the HGPRT from the child with Lesch-Nyhan disease?
Answer choices
- AThere is more HGPRT in the Lesch-Nyhan cells.
- BThere is an activating mutation in the HGPRT from the Lesch-Nyhan patient.
- CThe enzyme has a lower affinity for guanine than the control enzyme.Correct answer
- DThe gene for HGPRT is repressed in the Lesch-Nyhan patient.
- EA competitive inhibitor was added to the enzyme from the Lesch-Nyhan patient.
- FThe enzyme has an increased rate of product formation at saturating substrate concentrations.
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