Biochemistry

The second stage of dehydrogenation proceeds with the participation of NAD dependent dehydrogenase with the formation of f-keto acid (f-ketoacyl-CoA). ОН 0 О .1 // // R-CH2-CH-CH2-C +FAD R-CH2-C-C.H2-C Y P a \ -FADH 2 * Y PH a \ SCoA О SCoA P-Oxyacyl-CoA P-Ketoacyl-CoA Then there is a thiolase reaction', the interaction of ketoacyl-CoA with acetyl- CoA. ОН О I И R-CH2-CH-CH2-C Y p a \ SCoA -riiscoA -FADHj* p-Oxyacyl-CoA R -СНз-С + \ SCoA Acyl-CoA О // СНз-С \ SCoA Acetyl-CoA О И As a result of this reaction, as consequence of the cleavage of p-ketoacyl, activated higher fatty acid shortened by two carbon atoms and a two-carbon fragment in the form of acetyl-CoA are released. The resulting acetyl-CoA is oxidized in the tricarboxylic acid cycle, and the activatedhigher fatty acid repeatedly goes through the entire p-oxidation path until the formation of the four- carbon compound butyryl-CoA, which in its turn is oxidized to two acetyl-CoA molecules. The energy effect of p-oxidation. The number of oxidation cycles that a higher fatty acid undergoes depends on the number of carbon atoms in its molecule. When one fatty acid molecule is oxidized, n/2 acetyl-CoA molecules are formed, where n - is the number of carbon atoms, and the cycle repeats (n/2 - 7) times, because the butyryl-CoA molecule is immediately split into two acetyl-CoA molecules. In each cycle, the molecule FADH 2 and the molecule NADH 2 appear. During oxidation in the respiratory chain and conjugated phosphorylation, the FADH2 molecule produces two ATP molecules, and NADH 2 - three ATP molecules, i.e., five ATP molecules are formed in a single p-oxidation cycle. Each molecule of acetyl-CoA is included in the tricarboxylic acid cycle, is gradually split into CO 2 and H 2 O with the release of 12 ATP molecules. As an example, lets consider the P-oxidation of palmitic acid. 197