Decarboxylation pyruvate and

Figure 2. Mechanism of PDH. The three different subunits of the PDH complex in the mitochondrial matrix (E, pyruvate decarboxylase E2, dihydrolipoamide acyltrans-ferase Ej, dihydrolipoamide dehydrogenase) catalyze the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2. E, decarboxylates pyruvate and transfers the acetyl-group to lipoamide. Lipoamide is linked to the group of a lysine residue to E2 to form a flexible chain which rotates between the active sites of E, E2, and E3. E2 then transfers the acetyl-group from lipoamide to CoASH leaving the lipoamide in the reduced form. This in turn is oxidized by E3, which is an NAD-dependent (low potential) flavoprotein, completing the catalytic cycle. PDH activity is controlled in two ways by product inhibition by NADH and acetyl-CoA formed from pyruvate (or by P-oxidation), and by inactivation by phosphorylation of Ej by a specific ATP-de-pendent protein kinase associated with the complex, or activation by dephosphorylation by a specific phosphoprotein phosphatase. The phosphatase is activated by increases in the concentration of Ca in the matrix. The combination of insulin with its cell surface receptor activates PDH by activating the phosphatase by an unknown mechanism.

The biochemistry of this process represents another variation on the metabolism of glucose under anaerobic conditions. C. acetobutylicum can decarboxylate pyruvate and synthesize a thioester of acetate, acetyl coenzyme A. From this process it can derive more energy as ATP with the... 

The addition of thiamine is legal in several countries (EU, at a dose of 50 mg/hl) but it is rarely used to accelerate fermentation in winemaking. It effectively decreases significant ketonic acid concentrations by decarboxylation (pyruvic and a-ketoglutaric acid). Large quantities of these acids bind to sulfur dioxide in botrytized sweet wines (Section 8.4.2). 

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