Two of the steps in the oxidative decarboxylation of pyruvate (steps 4 and 5 in the figure) do not involve any of the three carbonsof pyruvate, yet are essential to the operation of the pyruvate dehydrogenase (PDH) complex.CH3PyruvateHydroxyethylTPP1TPPTPPCHOH1CH32Pyruvatedehydrogenase,E₁CH3SHAcetyllipoyllysine515CoA-SH CH3- C-S-COAAcetyl-CoAOxidizedlipoyllysine.Reduced3lipoyllysineDihydrolipoyltransacetylase,E₂LysFAD-SHSHFADH₂Dihydrolipoyldehydrogenase,E3NADH + H+NAD+ Why are steps 4 and 5 essential to the operation of the PDH complex?O They catalyze the synthesis of hydroxyethyl thiamine pyrophosphate (TPP).They transfer a thiol group from coenzyme A to acetyl lipoyllysine.They reoxidize the reduced lipoamide cofactor.They reduce the disulfide bond in oxidized lipoyllysine.

Pyruvate dehydrogenase (PDH) complex oxidizes pyruvate to acetyl-CoA and carbon dioxide. It happens…

Why are steps 4 and 5 essential to the operation of the PDH complex? They catalyze the synthesis of hydroxyethyl thiamine pyrophosphate (TPP). They transfer a thiol group from coenzyme A to acetyl lipoyllysine. They reoxidize the reduced lipoamide cofactor. They reduce the disulfide bond in oxidized lipoyllysine.

Why are steps 4 and 5 essential to the operation of the PDH complex? They catalyze the synthesis of hydroxyethyl thiamine pyrophosphate (TPP). They transfer a thiol group from coenzyme A to acetyl lipoyllysine. They reoxidize the reduced lipoamide cofactor. They reduce the disulfide bond in oxidized lipoyllysine.

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter19: The Tricarboxylic Acid Cycle

Section: Chapter Questions

Problem 22P: Study Figure 19.18 and decide which of the following statements is false. Pyruvate dehydrogenase is...

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The same E1-Ez-E3 multienzyme structure found in the pyruvate dehydro- genase and the a-ketoglutarate dehydrogenase complexes is also used in the branched-chain a-ketoacid dehydrogenase complex, which participates in the catabolism of branched chain amino acids. Draw the reaction product when the following substrate is acted on by the branched chain a-keto acid dehydrogenase complex. H,C -C-COo- H,C
Remembering that the Pyruvate dehydrogenase complex and the alpha ketoglugarate complex catalyze similar reactions, please match the following terms with its description: Dihydrolipoyl dehydrogenase (E3) 1) an alpha-keto acid that undergoes oxidative decarboxylation 2) is analogous to the pyruvate dehydrogenase reaction in which there's an oxidative decarboxylation with a concomitant formation of an acyl-CoA thioester 3) is analogous to the pyruvate dehydrogenase reaction and the isocitrate dehydrogenase reaction in which there's an oxidative decarboxylation with a concomitant formation of an acyl-CoA thioester 4) catalyzes the oxidative decarboxylation of alpha ketoglutarate 5) regenerates active dihydrolipoyl transacetylase (E2) 6) catalyzes the oxidative decarboxylation of succinyl coa 7) catalyzes the oxidative decarboxylation of alpha isocitrate 8) catalyzes the formation of Succinyl CoA Alpha ketoglutarate The alpha ketoglutarate dehydrogenase complex Alpha ketoglutarate…
Because dichloroacetate inhibits the enzyme pyruvatedehydrogenase kinase, this compound has been used,with limited results, to treat lactic acidosis. The phosphorylation of the a-subunit of the pyruvate dehydrogenasecomponent of the pyruvate dehydrogenase complex bypyruvate dehydrogenase kinase causes complete loss ofenzymatic activity. Describe the theory behind the clinicaluse of dichloroacetate.
Briefly describe the biological rationale for each of the following allosteric phenomena: (a) activation of pyruvate carboxylase by acetyl-CoA; (b) activation of pyruvate dehydrogenase kinase by NADH; (c) inhibition of isocitrate dehydrogenase by NADH; (d) activation of isocitrate dehydrogenase by ADP; (e) inhibition of a-ketoglutarate dehydrogenase by succinyl-CoA; (f) activation of pyruvate dehydrogenase phosphatase by Ca2+.
The enzyme, dihydrolipoamide dehydrogenase is present in both pyruvate dehydrogenase complex and α-ketoglutarate dehydrogenase complex. What type of reaction is catalyzed by these complexes? Describe the role of dihydrolipoamide dehydrogenase in these reactions.
The mechanism for the conversion from alpha kytoglutarate into succinyl CoA by alpha-ketoglutare dehydrogenase is analogous to the pyruvate dehydrogenase mechanism. Draw and show the major intermediates and arrow pushing for the enzyme-catalyze process for the conversion of alpha-ketoglutarate to succinyl CoA. Note: the carbanion of thiamine pyrophosphate nucleophillically attacks C-2 of the alpha-ketoglutarate, i.e., the carbonyl carbon of that substrate.
What are the similarities and differences between the reactions catalyzed by pyruvate dehydrogenase and a-ketoglutarate dehydrogenase?
Arsenate (HAsO42-) can replace inorganic phosphate (Pi) in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase, causing Glyceraldehyde 3-phosphate to be directly converted to 3-phosphoglycerate (NADH is still formed). If a cell is expose to Arsenate, which of the following metabolites of glycolysis will not be detectable in the cell? 2-phosphoglycerate 3-phosphoglycerate Fructose 6-phosphate Glucose 6-phosphate 1,3-bisphosphoglycerate
Arsenate (HASO42-) can replace inorganic phosphate (Pi) in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase, causing Glyceraldehyde 3-phosphate to be directly converted to 3-phosphoglycerate (NADH is still formed). If a cell is expose to Arsenate, which of the following metabolites of glycolysis will not be detectable in the cell? 2-phosphoglycerate B 3-phosphoglycerate Fructose 6-phosphate Glucose 6-phosphate E 1,3-bisphosphoglycerate
Describe in detail the structure of the pyruvate dehydrogenase complex.
(a) The pyruvate dehydrogenase complex and the a-ketoglutarate dehydrogenase complex have common reaction mechanisms and catalyze chemically similar reactions. However, there are two enzymes that are critical for regulating the pyruvate dehydrogenase complex that are not found in the a-ketoglutarate complex dehydrogenase. What are these regulatory proteins and what is the re-sult of their catalytic action? (b) Through the metabolism of pyruvate and of isocitrate, CO2 is released with production of NADH. One of these metabolites undergoes oxidative decarboxylation while the other undergoes non- oxidative decarboxylation. On the basis of the structures of the reactant and product for both metabolites show why one reaction is oxidative while the other is non-oxidative even though NAD+ is reduced in both cases. (c) Using structural formulas for the reactions catalyzed by the pyruvate dehydrogenase complex, draw the structures of the corresponding intermediates of the reaction cata-lyzed by…