BIOGRAPHICAL MEMORANDA 



described as anaerobic oxidations. These are processes in which a sub- 

 strate can be oxidized under strictly anaerobic conditions with the 

 simultaneous reduction of certain mineral constituents of the medium. 

 Specific examples are the processes known as nitrate, nitrite, and sul- 

 phate reduction. Formerly these had been interpreted as reactions in 

 which the reducible component of the medium supplied the oxygen 

 necessary for the oxidation of the substrate; now they could more 

 properly be regarded as examples of substrate dehydrogenations with 

 nitrate, nitrite, or sulphate acting as the specific hydrogen acceptors. 

 Thus the oxidation of a particular substrate, H 2 A, could be envisaged 

 to take place with the participation of various acceptors, and the 

 several possibilities expressed by the over-all reaction equations : 



2H 2 A+ 2 -> 2A+ 2 H 2 0; 

 4 H 2 A+HN0 3 -> 4A+3H 2 0+H 3 N; 

 3 H 2 A+HN0 2 -> 3A+ 2 H 2 0+H 3 N; 

 4 H 2 A+H 2 S0 4 -> 4 A+ 4 H 2 0+H 2 S; 



obviously all of these represent special instances of the general equa- 

 tion: 



H 2 A+B-^ A+H 2 B 



These comparisons were particularly significant because they eventu- 

 ally suggested an explanation for the general mechanism of the meth- 

 ane fermentation which Kluyver, in his London lectures, had char- 

 acterized as 'the ultimo ratio in the domain of oxido-reduction. ... It 

 is obvious that the extreme form which can be conceived for such a 

 process will be, that part of the carbon atoms present in the substrate 

 attain their highest reduction stage, i.e. methane, another part of 

 these carbon atoms their highest stage of oxidation, i.e. carbon dioxide' 

 (p. 75). At that time Kluyver had to admit, however, that the 'mech- 

 anism of this type of fermentation is as yet quite unknown' (p. 76). 



But a comparative-biochemical consideration of the methane fer- 

 mentation as another anaerobic oxidation process later suggested that, 

 in analogy with the nitrate, nitrite, and sulphate reduction, the meth- 

 ane fermentation could be interpreted as a case of substrate oxidation 

 coupled with the reduction of carbon dioxide, a 'carbonate reduction' : 



4 H 2 A+C0 2 -> 4 A+2H 2 0+GH 4 



This hypothesis received strong support from Barker's [1936a] dis- 



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