Glyphosate, which inhibits the EPSP synthase reaction of theshikimic acid pathway, is a phosphonic acid derivative of glycine;hence its name (glycine phosphonate). Based upon your knowledgeof the EPSP synthase reaction (see pages 908–909), would youexpect the inhibition to be competitive or noncompetitive withrespect to each of the substrates? Briefly explain your answer.

The biochemical reaction to combine PEP and 3-phosphoshikimate (S3P) to give phosphate and…

Answered: Glyphosate, which inhibits the EPSP…

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter25: Nitrogen Acquisition And Amino Acid Metabolism

Section: Chapter Questions

Problem 22P

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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.
There is another class of aldolase enzymes known as Class II. These enzymes are found in fungi, algae, and some bacteria. This class differs for Class I in that these enzymes do not have a Lys residue associated with their active sites, but contain a divalent cation (usually Zn2+ or Fe2+) in the active site. Outline a possible mechanism for a Class II aldolase and explain the function of the metal ion in the reaction.
ATP is a (+) allosteric effector, and CTP is a (-) allosteric effector of theenzyme ATCase. Both of these heterotropic effectors bind to the regulatorysubunits on ATCase. The substrates of ATCase, aspartate and carbamoylphosphate, bind the enzyme active site with positive cooperativity (i.e.,they exert a “+” homotropic effect on activity). As the concentrations ofthe substrates change from values where [S] ≪ KM to values where [S] issaturating ([S]≫ KM), how will the binding constants for each of the twoallosteric effectors change? In other words, does ATP bind ATCase withhigher affinity when [S] is low or high? Does CTP bind ATCase with higheraffinity when [S] is low or high?
Hexokinase catalyzes the first step of glycolysis, in which glucose is phosphorylated to form glucose‑6‑phosphate. Give two reasons why a Mg2+ cation is required to facilitate this reaction.
Because of the position of arsenic in the periodic table, arsenate (AsO43- ) is chemically similar to inorganic phosphate and is used by phosphaterequiring enzymes as an alternative substrate. Organic arsenates are quite unstable, however, and spontaneously hydrolyze. Arsenate is known to inhibit ATP production in glycolysis. Identify the target enzyme, and explain the mechanism of inhibition.
During glycogen synthesis, glucose-1P is converted into a molecule called UDPG. This reaction also cleaves uridine triphosphate (UTP) forming uridine monophosphate and pyrophosphate (PPi). Provide four reasons why UTP can be used to power this reaction (no diagrams necessary).
One of the regulators of the TCA cycle is succinyl CoA. Discuss the rationale for this molecule to be used to regulate the TCA cycle [include chemical structures and chemical equations where appropriate]. What is an allosteric inhibitor? How does it operate? For what TCA enzymes does succinyl CoA act as an inhibitor? What is the metabolic role of succinyl CoA? So then why is this molecule a reasonable choice as an inhibitor of the TCA?
Aminolevulinate (ALA) synthase is a pyridoxal phosphate containing enzyme displaying a non-sequential (ping-pong) enzyme mechanism. It catalyses the reaction: glycine + succinyl-CoA ⇌ aminolevulinate + CO2 Draw a Cleland diagram (diagram illustrating when the substrates and products form an enzyme substrate complex) for this reaction if glycine is the first substrate to bind.
In the hydrolysis of ATP to ADP and Pi, the equilibrium concentration of ATP is too small to be measured accurately. A better way of determining K’eq, and hence ΔG◦’ of this reaction, is to break it up into two steps whose values of ΔG◦’ can be accurately determined. This has been done using the following pair of reactions (the first being catalyzed by glutamine synthetase): (1) ATP + glutamate + NH3 ⇌ ADP + Pi + glutamine + H+ ΔG1◦’= -16.3 kJ/mol (2) glutamate + NH3 ⇌ glutamine + H2O + H+ ΔG2◦’= 14.2 kJ/mol What is the ΔG◦’ of ATP hydrolysis according to these data and is the overall reaction spontaneous? What is the value of the equilibrium constant for the overall reaction at 25.0 °C. If the concentration of ATP at equilibrium is 20.0 mM and the concentration of ADP at equilibrium is 50 nM. What is the concentration the phosphate group (in mM) at equilibrium?
A solution of the enzyme hexokinase incubated at 45 °C lost 50% of its activity in 12 min, but when incubated at 45 °C in the presence of a very large concentration of one of its substrates, it lost only 3% of its activity in 12 min. Suggest why thermal denaturation of hexokinase was retarded in the presence of one of its substrates. It is impossible for this result to be true. OA. Adding the substrate increases the weak forces that stabilize the enzyme. OB. The high concentration of substrate forms a barrier around the hexokinase. D. Adding the substrate results in protective covalent bonding.
The glutamate dehydrogenase (GDH) catalyses the following reaction: +H₂N- H - - CH₂ - CH₂ COO acide glutamique COO™® + NAD+ + H₂O GDH COO C: CH₂ CH₂ COO™ O + NH4+ NADH + H* The activity of GDH is monitored in the sense of the formation of glutamate using the following conditions: -0.2 mL of 5 M ammonium sulphate 2.4 mL of buffer at pH 8 0.1 mL of NADH at 6.15 mg.mL-¹ (M = 709 g.mol-¹) 0.2 mL of 1 M a-ketoglutarate solution Warm mixture at 25 °C for 5 min - Add 0.1 mL of GDH solution containing 1.6 mg.mL-¹protein to start the reaction. acide a-cétoglutarique The change in absorbance at 340 nm is monitored, in a 1-cm cuvette, every minute for 10 min. Results are given in the table below: Data: ENADH at 340 nm = 6220 M¹.cm¹ Time (min) 1 2 3 4 5 6 7 8 9 1.760 1.718 1.675 1.635 1.595 1.550 1.510 1.489 1.476 A340 10 1.451 - Draw the graph A = f(t). Calculate A340 at t = 0 and place this point on the curve. - Comment the shape of the curve, particularly the portion that corresponds to a…
What is the quaternary structure of glycogen phosphorylase? How would you characterize the allosteric effects of its small molecule substrate? (one word) What allosteric model (mechanism) that you have learned does it seem to follow? (one acronym)

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