2. Compare the Pyruvate Dehydrogenase Complex (Lord Figure 6.4 p332, Lp331-334)
ID: 182158 • Letter: 2
Question
2. Compare the Pyruvate Dehydrogenase Complex (Lord Figure 6.4 p332, Lp331-334) to the Branched Chain Ketoacid Dehydrogenase Complex (Lord Figure 4.12 p207). How are they similar and different in terms of functionality and nutrient requirements (make sure to read the text sections to understand this) What organic acids are elevated when there is insufficient activity of the Pyruvate Dehydrogenase Complex (PDC) vs the Branched Chain Ketoacid Dehydrogenase Complex (BCKDC)? (Make sure to understand the difference between BKCDC and BCAA transaminase. These are two completely different enzymes in the BCAA degradation pathway) 1 pointExplanation / Answer
Pyruvate Dehydrogenase Complex and Branched Chain Ketoacid Dehydrogenase Complex comparision:
The conversion of pyruvate to acetyl-CoA is done through a process known as pyruvate decarboxylation, as a result of oxidation of pyruvate. The PDH is a complex of three enzyme system that facilitates the conversion of pyruvate (end product of glycolysis) to acetyl-CoA. This process of irreversible conversion of pyruvate to acetyl-CoA is an important step in metabolic pathway, in the production of energy through cellular respiration.
The Branched-chain alpha-keto acid dehydrogenase complex (BCKDC) catalyzes irreversible catabolism of branched-chain amino acids L-isoleucine, L-valine, and L-leucine at mitochodrial inner membrane in animals. It helps in synthesis of long chain fatty acids by catalyzing L-isoleucine in bacteria. Like PDC, BCKDC also consists of three catalytically components; alpha-ketoacid dehydrogenase (E1), dihydrolipoyl transacylase (E2), and dihydrolipoamide dehydrogenase (E3).
Pyruvate dehydrogenase deficiency is reported to be responsible for hyper build up of lactic acid and pyruvate in body. This leads to lactic acidosis. Deficiency in any of BCKDC enzymes is shown to be associated with build of branched-chain amino acids. Pathological condition like maple syrup urine disease is known to be caused in such conditions.
The activity of the pyruvate dehydrogenase complex depends on the phosphorylation state of the enzyme. It is most active in its dephosphorylated state. Phosphorylation is carried out through phosphatases, while, the dephosphorylation process is carried out through kinases. The activity of the kinase enzyme would be increased with the cell contains high energy compounds like ATP, NADPH, and acetyl-CoA.
The PDC depends on product of glycolysis to function and thus effectively depending on glucose, BCKDC functions on availability of branched amino acids. Unlike BCKDC, BCAA transaminase (BCAT) catalyses first step of branched chain amino acid degradation pathway. These exhibit reversible transaminase activity on branched chain amino acids and mark them for oxidative decarboxylation.
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