Biosynthesis of Acetyl CoA

A The main entry point for the TCA cycle is through generation of acetyl CoA by oxidative decarboxylation of pyruvate. 

Pyruvate derived from glycolysis or from catabolism of certain amino acids is transported from the cytoplasm into the mitochondrial matrix. 

A specialized pyruvate transporter is responsible for this step. 

PDH removes CO2 and transfers the remaining acetyl group to the enzyme-bound coenzyme thiamine pyrophosphate, 

Dihydrolipoyl transacetylase transfers the acetyl CoA to its lipoic acid 

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The loss of the relatively C-enriched carbon atoms C-3 and C-4 of glucose [107], and the kinetic isotope effect on the pymvate-dehydrogenase reaction /7 0(5/ in the biosynthesis of acetyl-CoA have for consequence that isoprenoids from the MA-pathway are depleted in relative to carbohydrates from the same source by 4 to 6%o, whereas this C-depletion attains in products from the DOX-pathway only 2 to 4%o. C-pattems of the two types of isoprenoids, which would certainly be different, are still not yet available. 

Nitrosohydrazones from culture filtrates of Strepto-myces sp. SK 1894, e.g., T. B CnHijNjO, Mr 205.26, yellow powder, mp. 144-147 °C T. A C,H,9N)0, Mr 209.29, yellow powder, mp. 116-118°C. T. inhibit various acyl-CoA synthetases, e.g., arachidonoyl-CoA synthetase and the synthetases of longer-chain fatty acids the biosynthesis of acetyl-CoA remains unaffected. Common structural feature of the T. is the -N-hydroxy-l-triazene unit, bound to an unsaturated aliphatic chain. 

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