GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

11. FUNDAMENTAL MECHANISMS OF METABOLISM AND ENERGY TRANSFORMATION IN MICROORGANISMS

11.6. THE RESPIRATORY CHAIN AND PHOSPHORYLATION (ATP SYNTHESIS) DURING ELECTRON TRANSFER

There are Two main mechanisms of ATP synthesis: substrate-level phosphorylation and electron transport phosphorylation. While most anaerobic microorganisms are capable of synthesizing ATP exclusively via substrate-level phosphorylation, aerobes can regenerate ATP much more efficiently. They possess a specialized apparatus: the respiratory (electron transport) chain and the enzyme ATP synthase. In prokaryotes, both systems are located in Cell/30.html">The Plasma Membrane, whereas in eukaryotes, they reside on The inner mitochondrial membrane.

The oxidation of substrates generates reducing equivalents (protons and electrons), which enter the Respiratory Chain as NADH (in the case of organic substrate oxidation). The primary source of NADH during the growth of microorganisms on glucose is The Tricarboxylic Acid Cycle. Additionally, NADH is produced in the initial reactions of Glucose Catabolism:

at the stage of 1,3-diphosphoglycerate formation from glyceraldehyde-3-phosphate during glucose catabolism via the glycolytic and KDPG pathways;

during the oxidation of glucose to gluconate via the action of NAD⁺-dependent glucose dehydrogenase.

Energy is released in the respiratory chain during the oxidation of NADH (i.e., upon The transfer of electrons from NADH to oxygen or another electron acceptor), which is subsequently utilized for ATP synthesis.

Besides NADH, succinate also serves as an electron donor for the respiratory chain. One of the TCA cycle Enzymes, succinate dehydrogenase, oxidizes succinate to fumarate. Succinate dehydrogenase transfers electrons from succinate to FAD, from which the electrons then enter the respiratory chain.

To understand how ATP synthesis is coupled with electron transfer, it is necessary to examine: the Components of the respiratory chain; their redox potentials; and the spatial arrangement of these components within the membrane.