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Chapter 26: Problem 16

Enzymes that bind phosphoribosyl-5-phosphate (PRPP) have a common structural fold, the PRT fold, which unites them as a structural family. PRT here refers to the phosphoribosyl transferase activity displayed by some family members. Typically, in such reactions, \(\mathrm{PP}_{\mathrm{i}}\) is displaced from PRPP by a nitrogen-containing nucleophile. Several such reactions occur in purine metabolism. Identify two such reactions where the enzyme involved is likely to be a PRT family member.

Short Answer

Expert verified
Two reactions in purine metabolism that likely involve PRT family member enzymes are: 1) The reaction catalyzed by Adenine phosphoribosyltransferase (APRT), leading to the formation of AMP. 2) The reaction catalyzed by Hypoxanthine-guanine phosphoribosyltransferase (HGPRT), leading to the formation of IMP.

Step by step solution

01

Understand the Concept of PRT Enzymes

PRT enzymes are a family of enzymes that have a common structural fold, the PRT fold, which allows them to bind to phosphoribosyl-5-phosphate (PRPP). These enzymes show phosphoribosyl transferase activity, meaning they are capable of transferring a phosphoribosyl group from PRPP to an acceptor molecule, often aided by a leaving group, such as pyrophosphate (\(PP_{i}\)). In this context, the nitrogen-containing nucleophile is the acceptor molecule.
02

Consider the Role of PRT Enzymes in Purine Metabolism

In purine metabolism, several reactions occur where \(PP_{i}\) is displaced from PRPP by a nitrogen-containing nucleophile, facilitated by a PRT enzyme. Given the characteristics of the PRT enzyme, it is plausible that the nitrogen-containing nucleophile will be a purine base, or a precursor molecule thereof. Therefore, the reactions that will be focused on involve PRPP and a nitrogen-containing nucleophile and result in purine base or purine base precursors.
03

Identify Two Such Purine Metabolic Reactions Involving PRT Enzymes

Two such reactions in purine metabolism where a PRT enzyme is likely involved are:1. Reaction catalyzed by Adenine phosphoribosyltransferase (APRT): In this reaction, adenine (a nitrogen-containing nucleophile) displaces \(PP_{i}\) from PRPP, resulting in the formation of AMP (adenosine monophosphate), a crucial molecule in energy transfer.2. Reaction catalyzed by Hypoxanthine-guanine phosphoribosyltransferase (HGPRT): In this reaction, hypoxanthine (a nitrogen-containing nucleophile) displaces \(PP_{i}\) from PRPP to form IMP (inosine monophosphate), an intermediate in the synthesis of purine nucleotides.

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Most popular questions from this chapter

Draw the purine and pyrimidine ring structures, indicating the metabolic source of each atom in the rings.

(Integrates with Chapters \(18-20 \text { and } 22 .)\) By what pathway(s) does the ribose released upon nucleotide degradation enter intermediary metabolism and become converted to cellular energy? How many ATP equivalents can be recovered from one equivalent of ribose?

Indicate which reactions of purine or pyrimidine metabolism are affected by the inhibitors (a) azaserine, (b) methotrexate, (c) sulfonamides, (d) allopurinol, and (e) 5 -fluorouracil.

Illustrate the key points of regulation in (a) the biosynthesis of IMP, AMP, and GMP; (b) \(E .\) coli pyrimidine biosynthesis; and (c) mammalian pyrimidine biosynthesis.

Write a balanced equation for the oxidation of uric acid to glyoxylic acid, \(\mathrm{CO}_{2},\) and \(\mathrm{NH}_{3}\), showing each step in the process and naming all of the enzymes involved.
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