Terminal Oxidation The Cytochrome Chain

The mechanism by which oxygen became involved in respiration was discovered in outline between 1920 and 1939 although important 

Simultaneously with the elucidation of the tricarboxylic acid cycle was the discovery of the means by which oxygen was utilized in cells for terminal oxidation. An abortive start on this had been made by MacMunn (1886), a medical practitioner and the author of a major text on spectroscopy. In a paper for the Royal Society (1886) MacMunn had concluded  

The lethal effects of carbon monoxide on hemoglobin had been analyzed by Claude Bernard and shown to be due to the formation of an iron-carbonyl compound. In 1891 Mond and Langer showed that iron pentacarbonyl could be dissociated by light, and in 1897 J.S. Haldane and J.L. Smith found light would decompose the carbonyl compound of hemoglobin. Other metal carbonyls are not photodecomposed. 

The link between the dehydrogenation of tricarboxylic acid cycle substrates and oxygen uptake was clarified by Keilin between 1925 and 

The use of the reversion spectroscope enabled the position of the absorption bands to be determined accurately and to be conclusively distinguished from hemoglobin and myoglobin. It became clear that there were three different intracellular respiratory catalysts— cytochromes a,b,c—common to animals, bacteria, yeast and higher plants. In 1925 a preliminary scheme for the passage of O2 from blood to tissue was proposed  

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