In the salvage of purines, hypoxanthine-guanine phosphoribosyltransferase (HGPRT)is responsible for which of the following processes?Conversion of hypoxanthine to xanthineConversion of adenine to adenosine monophosphate (AMP)Conversion of guanine to guanosine monophosphate (GMP)Conversion of inosine monophosphate to inosine

Purines are heterocyclic rings made up of a five-membered ring fused to a six-membered ring.…

Answered: In the salvage of purines,…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Thiopurine S-methyltransferase (TPMT) is an enzyme that is responsible for the metabolism of the drugs azathioprine and 6-mercaptopurine, which are used to treat acute lymphoblastic leukemia and inflammatory bowel disease. Metabolism by TPMT reduces the bioavailability of the drugs. In addition to the thiopurine substrates, TPMT also binds S-adenosyl methionine as a cofactor. TPMT is a highly polymorphic enzyme; almost 30 variants are known to be expressed in humans, with most of the variants possessing lower enzymatic activity than the wild-type protein (TPMTwt). Despite having substitutions remote from the active site, TPMT*2 (an A80P variant) and TPMT*5 (an L49S variant) have enzyme activities of 47% and 14% relative to TPMTwt at 18°C, respectively. Two techniques were used to understand the relationships between enzymatic activity and protein stability. Circular dichroism (CD) spectroscopy measures the differential absorption of left and right-circularly polarized light and is used…
Diisopropylphosphofluoridate (DIPF) inactivates chymotrypsin by covalently modifying serine 195. Which statement is true of DIPF's inhibitory mechanism? DIPF randomly modifies all serine residues on the protein, and if enough is added, the serine in the active site will eventually be modified. DIPF approaches serine 195 more closely than other substrates. DIPF looks like the substrate for chymotrypsin and binds in the active site as a competitive inhibitor. Serine 195 is in an environment that gives it a higher than normal reactivity with respect to DIPF.
Why is de novo biosynthesis of purines markedly elevated in patients with a deficiency in hypoxanthine-guanine phosphoribosyl transferase (HGPRT)? 5-Fluoruracil is converted to methotrexate by a DPD deficiency, leading to increased purine biosynthesis. HGPRT deficiency prevents purine salvage, leading to increased purine biosynthesis to make up for it. HGPRT increases pyrimidine salvage and thereby increases purine biosynthesis as a result. Increased purine biosynthesis is the result of ATP hydrolysis during the production of cyclic AMP.
Which of the following about adenosine triphosphate (ATP) is FALSE? A) There are two phosphoanhydride bonds with similar energies B) ATP can be used as a substrate to make cyclic AMP (cAMP) after a cell has been stimulated with certain specific hormones C) The γ-phosphate can be transferred (e.g. to chemical group on a protein enzyme) such as the Na+-K+ pump, which is part of a coupling mechanism that allows otherwise unfavourable reactions to proceed No possible answer provided E) The large, negative, free-energy change upon hydrolysis of “high-energy” compounds like ATP is partly due to the creation of resonance stabilized products
You have isolated a new protease that cleaves peptide bonds on the carboxyl side of Asp and Glu. Based on the enzyme's inactivation by DIPF, you suspect that it may utilize a mechanism similar to chymotrypsin. The difference in specificity might be explained by the absence of the S1 binding pocket. replacement of serine 195 with a positively charged residue. presence of a positively charged residue in the S1 binding pocket. presence of a negatively charged residue in the S1 binding pocket.
Folic acid is synthesized in bacteria as dihydrofolate, in a pathway starting from guanosine triphosphate. In this pathway, C-8 is lost as formate. From the structural similarities between guanine and pterin, predict which carbon and nitrogen atoms of GTP are the precursors to N-1, C-2, C-4, N-5, C-7, N-8, and C-9 of dihydrofolate.
When hyaluronan synthase from Pasteurella multocida was expressed in E. coli, the bacteria spun out a capsule of hyaluronan. This reaction was analyzed using purified membrane fragments containing the hyaluronan synthase, a radio-labeled tetrasaccharide acceptor (Part A), along with the activated forms of the sugar subunits: UDP-N-acetylglucosamine and UDP-glucuronic acid. In short incubations with the complete mixture, the tetrasaccharide primer elongated by several units, although only odd-numbered chains were visible (Part B lane 2). If one or both activated sugars were left out, the results shown in lanes 3-5 (Part B) were obtained. Why do you suppose that only odd-number chains are visible in your assay? (A) ACCEPTOR nonreducing end HO- HO OH COO glucuronic acid (GICUA) HO- CH3 T C=O I NH CH₂ OH N-acetylglucosamine (GlcNAc) COO но- HO OH OH I CH₂ reducing end NH C=O CH3 Choose one: O A. Synthase adds GlcNAc much more slowly than it adds GICUA. O B. One of the monosaccharide…
Peroxidase is an enzyme found in many organisms, from plant to humans. The function of peroxidase is to break down hydrogen peroxide, which is a toxin produced as a byproduct when oxygen is produced during respiration. Myeloperoxidase is a protein found in neutrophils and catalyzes lipid peroxidation involved in immune defense. The overproduction of myeloperoxidase has been found to function as a mediator for tissue damage in inflammatory diseases. (8 points) a. Identify two examples of environmental factors that may impact myeloperoxidase activity. Describe how each of the environmental factors would affect the reaction rate of the enzyme. b. Predict the how researchers can use myeloperoxidase activity as oxidative stress biomarkers in patients with rheumatoid arthritis. Provide reasoning to justify your prediction.
ATP synthase is a protein that catalyzes the formation of the energy storage molecule adenosine triphosphate using adenosine diphosphate and inorganic phosphate. Which of the following are true for the protein, ATP synthase? Select all apply A mutation of Asp61 to glutamic acid would have less of a deleterious effect on its ability to synthesize ATP than a mutation of Asp61 to alanine A mutation of Asp61 to alanine would have less of a deleterious effect on its ability to synthesize ATP than a mutation of Asp61 to glutamic acid The F1 subunit is primarily responsible for translocating H+ ions across the inner mitochondrial membrane during ATP synthesis The FO subunit is primarily responsible for translocating H+ ions across the inner mitochondrial membrane during ATP synthesis
Some bacteria contain three different forms of aspartokinase, each with its own mode of regulation. Based on the roles of aspartoki- nase, as discussed in the text, propose a regulatory scheme applicable to each form of aspartokinase.
A bacterial lactose transporter, which is highly specific for lactose, contains a Cys residue that is essential to its transport activity. Covalent reaction of N-ethylmaleimide (NEM) with this Cys residue irreversibly inactivates the transporter. A high concentration of lactose in the medium prevents inactivation by NEM, presumably by sterically protecting the Cys residue, which is in or near the lactose-binding site. You know nothing else about the transporter protein. Suggest an experiment that might allow you to determine the Mr of this Cys-containing transporter polypeptide.
d) Alcohols usually don't behave as a weak acids, but tyrosine does. Explain why Y ionizes, while S and T do not. e) Is Y ionization physiologically relevant? Explain. f) Y is capable of being phosphorylated by kinases in vivo. What mutation might you introduce to render Y unphosphorylatable? Constitutively phosphorylated?

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