Biochemistry: The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

On how electrons meet oxygen, how ATR is generated in the process, and some related phenomena
Utilization of energy from inorganic reactions

Some Bacteria derive all of their energy from inorganic reactions (Ch. 1, Sec. A,10). The METABOLISM of these chemolithotrophic organisms is generally related to that of heterotrophic organisms, but they possess the additional capacity to obtain energy from an inorganic process. They also have The ability to fix CO₂, much like green plants. Chloroplasts of green plants, utilizing solar energy, supply the Organism with both ATP and the reducing agent NADH. Similarly, lithotrophic bacteria must obtain both energy and reducing agents from inorganic reactions.

As a rule, lithotrophic organisms are characterized by slow growth, and studying their metabolism presents significant difficulties [109]. Nevertheless, from what is already known, it is quite evident that in most cases these bacteria possess an Electron Transport Chain that is in many respects similar to the corresponding mitochondrial system. Electron transport along this chain leads to the generation of ATP. The amount of ATP synthesized depends on the number of coupling sites, which in turn depends on the electrode potentials of the reactions involved. Thus, The oxidation of H₂ by O₂ drives electron transport through all three coupling sites, resulting in the synthesis of three ATP molecules. On the other hand, the oxidation of nitrite by O₂, for which E⁰' (pH 7) = +0.42 V, leads to ATP synthesis only at site III. During nitrite oxidation, not only is the ATP yield lower than during H₂ oxidation, but another problem also arises. While reduced pyridine NUCLEOTIDES are easily generated at the expense of H₂, nitrite is not a strong enough reducing agent to reduce NAD⁺ to NADH. The only way that reducing equivalents can be generated in Cells utilizing this reaction is through reverse electron flow driven by ATP Hydrolysis. Reverse electron flow is a process characteristic of many chemolithotrophic organisms.

Let us consider two groups of inorganic reactions: 1) the oxidation of Reduced Inorganic Compounds by O₂ and 2) oxidation reactions in which other inorganic oxidants, such as nitrate or sulfate, are used instead of O₂. Reactions of the second group are often referred to as Anaerobic Respiration.