Biological oxidation is preceded by a degradation of substrates to form bound hydrogen and CO2
The overall reaction of biological oxidation is equivalent to a combustion of substrates. In contrast to technical combustion, however, biological oxidation proceeds in a sequence of partial reactions, which allows the utiliza-tion of the major part of the free energy for ATP synthesis.
The principle of biological oxidation was formulated in 1932 by the Nobel Prize winner Heinrich Wieland (Germany):
XH2 + 1/2O2 → X + H2O
First, hydrogen is removed from substrate XH2 and afterwards oxidized to water. The oxidation of carbohydrates [CH2O]n involves a degradation by reaction with water to form CO2 and bound hydrogen [H], which is oxi-dized to water:
[CH2 O] + H2O → CO2 + 4[H]
4[H] + O2 → 2H2O
In 1934 Otto Warburg (Berlin, winner of the 1931 Nobel Prize in Medicine) showed that the transfer of bound hydrogen from substrates to the site of oxidation occurs in the form of NADH. From studies with homogenates from pigeon muscles, Hans Krebs formulated the citrate cycle (also called the Krebs cycle) in England in 1937, as a mechanism for sub-strate degradation yielding NADH for biological oxidation. In 1953 he was awarded the Nobel Prize in Medicine for this discovery.