Concept explainers
Distinguishing the Mechanisms of Class I and Class I Aldolases
Fructose bisphosphate aldolase in animal muscle is a class 1 aldolase, which forms a Schiff base intermediate between substrate (for example. fructose-1, 6-bisphosphate or dihydroxyacetone phosphate) and a lysine at the active site (see Figure I8.12). The chemical evidence for this intermediate conies from studies with aldolase and the reducing agent sodium borohydride, NaBH4. Incubation of the enzyme with dihydroxyacetone phosphate and NaBH4 inactivates the enzyme. Interestingly, no inactivation is observed if NabH4 is added to the enzyme in the absence of substrate. Write a mechanism that explains these observations and provides evidence for the formation of a Schiff base intermediate in the aldolase reaction.
Want to see the full answer?
Check out a sample textbook solutionChapter 18 Solutions
Biochemistry
- Extending the Mechanism of Methylmalonyl-CoA Mutase to Similar Reactions Based on the mechanism for the methylmalonyl-CoA mutase (see problem 14), write reasonable mechanisms for the following reactions shown.arrow_forwardUsing the ActiveModel for enoyl-CoA dehydratase, give an example of a case in which conserved residues in slightly different positions can change the catalytic rate of reaction.arrow_forwardGlucosidase I catalyzes hydrolysis of specific glucosidase I is a synthetic trisaccharide, glucose-al-2- glucose-al-3-glucose-a-O(CH₂) #COOCH3. Kinetic measurements oligosaccharides containing glucose. obtained using this trisaccharide as substrate in the deoxynorjirimycin at concentrations of 50 μM (), 100 μM absence (x-x) and presence of the inhibitor 1- A) were used to prepare the (-), and 200 μM (4 Lineweaver-Burk plot below: b) Page 3 12) 7. a) V/V (nmol/hr)-1 1.S 1.0- 0.5 1/Trisaccharide (mM)-! Estimate the values for Vmax and KM for the trisaccharide substrate in the absence of the inhibitor. 0.0 -1.0 0.0 One substrate for 1.0 2.0 Determine whether inhibition by 1-deoxynorjirimycin is competitive, non-competitive or neither.arrow_forward
- The muscle isozyme of lactate dehydrogenase is inhibited by lactate. Steady state kinetic analysis yielded the following data, with lactate either absent or present at a fixed concentration.arrow_forwardThe interconversion of DHAP and GAP greatly favors the formation of DHAP at equilibrium. Yet the conversion of DHAP by triose phosphate isomerase proceeds readily. Whyarrow_forwardUsing the principles described in the text regarding pyridoxal phosphate mechanisms, propose a mechanism for the reaction catalyzed by serine hydroxymethyltransferase.arrow_forward
- Based on the action of thiamine pyrophosphate in catalysis of the pyruvate dehydrogenase reaction, suggest a suitable mechanism for the fourth step in the pyruvate decarboxylase reaction in yeast:arrow_forwardOne treatment for hyperuricemia is administration of xanthine oxidase inhibitors like allopurinol. What is the biochemical rationale for this treatment? Discuss the mechanism and show an illustration how this drug able to alleviate symptoms of hyperuricemia?arrow_forwardThe mitochondrial form of carbamoyl phosphate synthetase is allosterically activated by N-acetylglutamate. Briefly describe a rationale for this effect.arrow_forward
- Phosphonacetyl-L-aspartate (PALA) is a potent inhibitor of aspartate transcarbamoylase because itmimics the two physiological substrates of the enzyme. However, in the presence of substrates, lowconcentrations of PALA increase the reaction rate of aspartate transcarbamoylase. Explain this result.arrow_forwardIn the first step of the aldolase reaction, an active site Lys229 residue, with its side chain amino group in the deprotonated state, acts as a nucleophile and attacks the carbonyl C2 carbon of fructose 1,6-bisphosphate to form a Schiff base (boxed in the scheme). Since the pKa of the Lys side chain amino group in free solution is ~10.5, the pKa of Lys229 side chain must have been perturbed to a (higher lower) value for the enzyme to be active at neutral pH. the answer should include sufficient details, including the definition of pKa.arrow_forwardThe reaction catalyzed by malate dehydrogenase has a ΔG°′ value of +29.7 kJ⋅mol−1. Given what this says about the occurrence of the reaction catalyzed by malate dehydrogenase in cells explain how the reaction catalyzed by citrate synthase (−31.5 kJ⋅mol−1) influences that activity of malate dehydrogenase. In addition, explain how the activity of citrate synthase functions as a regulatory point for the citric acid cyclearrow_forward
- BiochemistryBiochemistryISBN:9781305577206Author:Reginald H. Garrett, Charles M. GrishamPublisher:Cengage Learning