Biochemistry

COOH о • ■ OO I CH, COOH H,° I соон >^ 9 H I CH, Z I - HOC-COOH CH 3 CO~SCoA Acetyl-CoA соон Pyruvate (pyruvic acid) соон Citrate (citric acid) COOH H,O -J C-COOH J HC I COOH cis-Aconitic acid соон I Oxaloacetate (oxalylacetic acid) COOH I HCOH I CH, . I - COOH Malate (malic acid) Fumarate (fumaric acid) COOH соон X соон CH, H-C-COOH HOCH I COOH Isocitrate (isocitric acid) a-Ketoglutarate Y Hj (a-ketoglutaric acid) C~o COOH GDP+ P n . / К — 2H coo T H/Z® {н, /к И CH, I 2 COOH Succinate (succinic acid) Figure 11.6 - Tricarboxylic acid cycle Consequently, 4 NADH 2 molecules (12 ATP molecules), 1 FADH 2 molecule (2 ATP molecules) and 1 ATP molecule are formed from a single triose in the aerobic cycle. Since 2 trioses form from a single glucose molecule, the energy output will be 15 x 2 = 30 ATP molecules, and the complete oxidation of 1 glucose molecule in the anaerobic and aerobic cycles will be 8 + 30 - 38 ATP molecules. The resulting oxalo-acetic acid can react with another acetyl-CoA molecule and the process starts over again. Thus, a certain amount of oxalo-acetic acid repeatedly participates in the reaction and provides oxidation to CO 2 and H 2 O of a large amount of acetic acid formed from carbohydrates, lipids, proteins and other compounds. But this process is not endless. Oxalo-acetic acid is decarboxylated in mitochondria with formation of pyruvic acid, which in its turn is converted to acetyl-CoA. 231