key term - Hypoxanthine-guanine phosphoribosyltransferase

Definition

Hypoxanthine-guanine phosphoribosyltransferase (HPRT) is an important enzyme involved in the purine salvage pathway, responsible for converting hypoxanthine and guanine into their respective nucleotides by attaching them to a ribose-5-phosphate moiety. This process recycles purines, allowing cells to conserve energy and resources by reusing bases instead of synthesizing them de novo. HPRT plays a critical role in maintaining nucleotide balance and is essential for proper cell function.

5 Must Know Facts For Your Next Test

1. HPRT catalyzes the transfer of a phosphoribosyl group from 5-phosphoribosyl-1-pyrophosphate (PRPP) to hypoxanthine or guanine, resulting in inosine monophosphate (IMP) or guanosine monophosphate (GMP), respectively.
2. Deficiency in HPRT activity leads to Lesch-Nyhan syndrome, a genetic disorder characterized by neurological impairment and self-injurious behavior due to excessive uric acid production.
3. The enzyme is predominantly expressed in the brain and lymphocytes, indicating its significance in maintaining cellular nucleotide levels in these tissues.
4. HPRT activity can be influenced by the availability of substrates like hypoxanthine and guanine, as well as PRPP concentration, highlighting its regulatory role in purine metabolism.
5. The salvage pathway, including HPRT, is crucial under conditions of rapid cell division or stress, when nucleotide synthesis demands increase.

Review Questions

• How does hypoxanthine-guanine phosphoribosyltransferase contribute to nucleotide metabolism?
  • HPRT contributes to nucleotide metabolism by facilitating the conversion of hypoxanthine and guanine into their respective nucleotides through the phosphoribosylation process. This function is part of the purine salvage pathway, which recycles purines, allowing cells to efficiently manage their nucleotide pools. By reusing existing bases instead of synthesizing them de novo, HPRT helps conserve energy and resources necessary for cellular functions.
• What are the implications of HPRT deficiency on human health, particularly concerning Lesch-Nyhan syndrome?
  • HPRT deficiency results in Lesch-Nyhan syndrome, which manifests as neurological dysfunction, self-mutilating behaviors, and hyperuricemia due to elevated uric acid levels from excessive purine breakdown. The lack of functional HPRT impairs the salvage pathway for purines, forcing cells to rely on de novo synthesis, which cannot meet the demands for nucleotides. This condition underscores the importance of HPRT in maintaining purine homeostasis in the body.
• Evaluate the role of hypoxanthine-guanine phosphoribosyltransferase in cellular stress situations requiring rapid nucleotide synthesis.
  • During cellular stress or rapid proliferation, the demand for nucleotides increases significantly. HPRT plays a vital role in meeting this demand by facilitating the salvage of hypoxanthine and guanine for nucleotide synthesis. By efficiently recycling purines through its enzymatic action, HPRT ensures that cells have an adequate supply of nucleotides needed for DNA and RNA synthesis. This not only supports growth and replication under stress but also helps maintain cellular integrity by preventing depletion of nucleotide pools.

Related terms

Purine Salvage Pathway: A metabolic pathway that recycles purines from degraded nucleotides and nucleic acids back into nucleotide synthesis, conserving energy and resources.

Adenine: A purine nucleotide that is an essential building block of DNA and RNA, playing vital roles in energy transfer as adenosine triphosphate (ATP).

Xanthine Oxidase: An enzyme that catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid, important in purine metabolism.