Question

Hypoxanthine in purine salvage pathways without HPRT

A) Is converted to uric acid
B) Is excreted unchanged
C) Is converted to xanthine
D) Is converted to adenine

Answer 1

Hypoxanthine is converted to uric acid in the purine salvage pathway when HGPRT is absent. The absence of HGPRT results in a failure to salvage purine bases, leading to their degradation into uric acid, notably in Lesch-Nyhan syndrome.

Step-by-step explanation:

Hypoxanthine in purine salvage pathways without Hypoxanthine Guanine Phospho Ribosyl Transferase (HGPRT) is converted to uric acid. The salvage pathway usually recycles purine bases like hypoxanthine and guanine into usable nucleotides through the action of HGPRT. However, in the absence of HGPRT, as seen in conditions like Lesch-Nyhan syndrome, hypoxanthine cannot be salvaged and is instead degraded to uric acid. This is confirmed by the pathophysiology of Lesch-Nyhan syndrome, where the lack of HGPRT leads to the accumulation of uric acid from unrecycled purines such as hypoxanthine and guanine.

In contrast, when HGPRT is functional, hypoxanthine would combine with 5-PRPP and be converted back into a purine nucleotide, specifically, IMP (inosine monophosphate). Without this enzyme, the conversion cannot occur and instead results in the overproduction of uric acid. Conditions with elevated levels of uric acid, such as gout, can result from excessive tissue destruction where nucleic acids are released and subsequently broken down into uric acid.