Biochemistry

During the fifth reaction, succinyl-CoA when interreacting with inorganic phosphate, reacts with guanidyl diphosphate (GDP) and turns into succinic acid, and the GDP combining phosphate change into GTP. z° COOH C~SKoA 1 1 CH 5 + H PO GDP 1 2 -> CH } CH 2 -HSCoA,GTP(ATP) 1 2 1 COOH COOH Succinyl-CoA Succinate (succinic acid) As a result of the sixth reaction, succinic acid with the participation of FAD is oxidized to fumaric acid (fumarate). The latter is hydrated to form malic acid(seventh reaction). Under the influence of NAD, it is oxidized to oxalo-acetic acid (oxaloacetate) — the eighth reaction, i.e., to the substrate from which the tricarboxylic acid cycle begins. COOH COOH 1 COOH COOH 1 CH, +FAD f H +H £ CH i CHOH 1 + NAD^ C=O 1 CHj - fad 4 СНг - NAD H* CHj COOH COOH COOH COOH Succinate (succinic acid) Fumarate (fumaric acid) Malate (malic acid) Oxaloacetate (oxaloacetic acid) The process of aerobic oxidation of carbohydrates occurs with the release of energy (due to NADH 2 and FADH). One molecule of NADH 2 is released at the stage of pyruvate decarboxylation with the formation of acetyl-CoA. The oxidation of isolimonic acid to oxalosuccinic acid is also accompanied by the release of the NADH 2 molecule. During the decarboxylation of a-ketoglutaric acid, succinyl-CoA and NADH 2 are formed. Succinyl-CoA is converted to succinic acid to form 1 molecule of A TP (due to GTP). The dehydrogenation of succinic acid occurs with the release of FADH 2 , and the dehydrogenation of malic acid occurs with the release of NADH 2 . It is known that 1 NADH 2 molecule is equivalent to 3 ATP molecules, and 1 FADH 2 molecule is equivalent to 2 ATP molecules (Fig. 11.6). 230