Draw a plausible mechanism for the oxidation of dihydrolipoamide to lipoamide by the E, subunit (dihydrolipoamide dehydrogenase) of pyruvate dehydrogenase complex.
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- Draw a plausible mechanism for the oxidation of dihydrolipoamide to lipoamide by the E3 subunit (dihydrolipoamide dehydrogenase) of pyruvate dehydrogenase complex.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.Considering the evidence that led Krebs to propose a cyclic pathway for oxidation of pyruvate, discuss the type of experimental evidence that might have led to realization of the cycdic nature of the glyoxy- late pathway.
- 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.Explain how pyruvate dehydrogenase regulated using covalent modification (E1) of pyuvate dehydrogenase complex can be (phosphorylation or dephosphorylation).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
- The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate, catalyzed by glyceraldehyde 3- phosphate dehydrogenase, proceeds with an unfavorable equilibrium constant ( K'eq= 0.08; ΔG′° = 6.3 kJ/mol), yet the flow through this point in the glycolytic pathway proceeds smoothly. How does the cell overcome the unfavorable equilibrium?Considering the evidence that led Krebs to propose a cyclic pathway for oxidation of pyruvate, discuss the type of experimental evidence that might have led to realization of the cyclic nature of the glyoxylate pathway.The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase has an unfavourable equilibrium constant (K'eq= 0.08; G′° = 6.3 kJ/mol), yet the flow at this point in the glycolytic pathway is smooth. How does the cell get out of the unfavourable equilibrium?
- Lactic acidosis, weakness, fatigue, and sleepiness are observed in patients with genetic defects of one if the enzymes of pyruvate dehydrogenase complex. Explain The causes of the elevation of lactate in the blood of such patients and the emergence of hypoenergetic state. For this purpose write the following: a) scheme of the metabolic pathway of glucose metabolism, that includes this reaction and calculates the energetic effect of the process, outlining the reactions coupled with the use and formation of ATP. b) reaction of the reduction of pyruvate and explain the reason for its acceleration inpatients that have such genetic defects.Describe in detail the structure of the pyruvate dehydrogenase complex.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: