Biochemistry

However, not all biological substrates are oxidized by oxygen in the presence of readily oxidizing substances and peroxidase. Based on the results of his research, the Russian chemist V.I.Palladin in 1908 developed a theory according to which the main role in biological oxidation is played by enzymes that catalyze the removal of hydrogen from organic substances of cells, i.e., dehydrogenases . The function of oxygen, according to this theory, is to oxidize hydrogen to form water. The theory of V.I.Palladin was further developed in the works of G.Wiland, who described how the oxidation of substances that are not direct substrates for the action of dehydrogenases occurs. Such a substance was called, for example, acetic aldehyde. At the beginning of the 20th century, two concepts developed: the biological activation of oxygen and the activation of hydrogen. However, the confrontation of their adherents did not last long. In 1925, D.Cailin discovered cytochromes in aerobic biological objects, i.e., missing enzymes, which allowed scientists several years later to bind the activation of oxygen and hydrogen together. This was facilitated by the discovery of O. Warburg ( 1928 ) of cytochrome oxidase, which is called the "respiratory enzyme of Warburg." It was cytochrome oxidase that turned out to be the enzyme that directly activates hydrogen, and cytochromes — enzymes that “ remove ” electrons from hydrogen and transfer them to cytochrome oxidase. The modem theory of biological oxidation has combined the theories of Bach - Warburg and Palladin - Wieland at a new level of development of research on this scientific problem. So, biological oxidation is the process of the removal of hydrogen atoms or electrons from a substrate and their transfer through a series of intermediate steps to molecular oxygen. The following enzymes take part in this process: pyridine-dependent dehydrogenases (nicotinamide adenine dinucleotide - NAD or nicotinamide adenine dinucleotide phosphate - NADP performs their coenzyme function), flavin-dependent dehydrogenases - flavin enzymes - flavin adenine dinadenide nucleotide; cytochromes (containing the iron-porphyrin ring system as a prosthetic group), as well as ubiquinone (coenzyme Q ) and proteins containing non-heminic iron. 4.2 ROLE OF OXIDATIVE REDUCING ENZYMES IN BIOLOGICAL OXIDATION Pyridine-dependent dehydrogenases. This group of catalysts includes complex enzymes, the non-protein part of which is NAD and NADP . In NAD cells, dependent dehydrogenases are involved mainly in processes associated with electron transfer from organic substrates to oxygen. 105