Fundamentals of Biochemistry - Filippovych, Y. B. 1999

Biological Oxidation
Classification of biological oxidation processes and their cellular localization

The brief historical sketch provided above contains enough specific material to make the existence of Two Types of Biological Oxidation quite clear.

1. Free Oxidation, uncoupled from ADP phosphorylation, which is not accompanied by the transformation of energy released during oxidation into the energy of high-energy bonds. In free oxidation, The energy released from the Cleavage of chemical bonds coupled with oxidation turns into heat and dissipates.

Free oxidation encompasses all oxygenase reactions without exception, all oxidative reactions accelerated by peroxidases or accompanied by The formation of H₂O₂, and many Reactions Catalyzed by oxidases.

Free oxidation processes are localized in the Cytosol, in the membranes of The Endoplasmic reticulum, Lysosomes, Peroxisomes, and the Golgi apparatus, as well as on the outer membranes of Cell/35.html">Mitochondria and METABOLISM/14.html">Chloroplasts. They also take place in the Cell Nucleus.

2. Oxidation coupled with ADP phosphorylation. This type of biological oxidation is carried out in two ways.

If a high-energy bond is formed at the moment of direct substrate oxidation and is subsequently transferred in one way or another to a phosphate residue, which in turn is used to phosphorylate ADP (i.e., synthesize ATP), this type of biological oxidation is referred to as oxidation coupled with ADP phosphorylation at the substrate level. Previously, this mechanism was called phosphorylating oxidation or substrate-level phosphorylation.

If hydrogen atoms from the Coenzymes of dehydrogenases involved in substrate oxidation are transferred to the oxidoreductase chain—where, coupled with The transfer of protons and electrons to molecular oxygen, inorganic phosphate is activated and subsequently used to phosphorylate ADP to form ATP—such Coupling of oxidation with ATP synthesis is called coupling at the Electron Transport Chain level. Naturally, the oxidized substrate itself does not directly participate in the activation of inorganic phosphate in this case. Previously, this type of biological oxidation was called Oxidative Phosphorylation AND was equated with Respiration.

The coupling of oxidation with phosphorylation—that is, the generation of ATP to meet cellular demands—occurs primarily on The inner mitochondrial membranes. It is precisely here that oxidation is coupled with phosphorylation at The electron transport chain level. As for substrate-level phosphorylation, it is localized in the soluble fraction of The Cell.

Photosynthetic and chemosynthetic ADP phosphorylation, accompanied by ATP Biosynthesis, also occurs through the coupling of electron transfer in Electron Transport Chains with the activation of inorganic phosphate. The Mechanism of this coupling is similar to that of oxidative phosphorylation in mitochondria, which emphasizes the common Nature of the processes leading to ATP Synthesis in heterotrophic and autotrophic organisms.