BIOCHEMISTRY OF MICRO-ORGANISMS 



109 



the rapid decomposition of phosphorylated 

 products. It is, therefore, important to 

 mention the recent work of Kruyk and 

 Klingmiiller (1939) which indicates that 

 the phosphorylation of sugar by the intact, 

 living yeast, and in the absence of sub- 

 stances which inhibit certain step reactions, 

 is highly probable. 



The micro-organisms are, again, largely 

 responsible for the development of another 

 concept which nowadays plays such a gov- 

 erning role in biochemical thought. This 

 is the concept that fundamentally all chem- 

 ical activities of living organisms must be 

 considered as hydrogen transference reac- 

 tions. Originally advanced by Bredig 

 and, particularly, by Wieland (1932), this 

 hypothesis was developed on the basis of 

 analogies existing between the purely 

 chemical reactions of alcohol and of acetal- 

 dehyde with oxygen in the presence of 

 platinum or palladium catalysts, and the 

 oxidation of alcohol to acetic acid under 

 the influence of acetic acid bacteria. These 

 similarities led Wieland to postulate that 

 respiration consists primarily of a dehy- 

 drogenation of the respiratory substrate 

 with oxygen acting as the final hydrogen 

 acceptor, replaceable, however, by a num- 

 ber of other acceptors. 



The general aspect of this theory of res- 

 piration has long been disputed by War- 

 burg, who stressed the function of oxygen- 

 activation by iron. But von Szent Gyorgyi 

 (1924), Fleisch (1924), and Kluyver and 

 Donker (1926) have ably defended the 

 thesis that Wieland 's and Warburg's the- 

 ories do not represent two fundamentally 

 different and irreconcilable points of view 

 but that, at least in respiratory (oxidative) 

 metabolism, they are complementary. In 

 the hands of Kluyver and his school Wie- 

 land 's concept has been expanded to its 

 broadest generalization : the comprehensive 

 survey of microbial metabolism made it 

 possible to formulate the viewpoint that 

 each one of the steps involved in all bio- 

 chemical processes can be represented by 

 one or more of the following fundamental 

 hydrogen transference reactions : 



AH + B ^ A + BH 



AH.B -^ A.BH 



AH.B-^A + BH 

 AH + B ^ A.BH^ 



It may here be added that the brilliant 

 investigations of Warburg (1937) have 

 recently proved the intrinsic correctness of 

 this general formulation. Even the en- 

 zymes that have so far been studied in this 

 connection behave like components of an 

 AH + B system (Warburg 1937). 



The great value of this general point of 

 view has been demonstrated in clarifying 

 a large variety of metabolic processes. 

 Through its application it became possib^le 

 to consider several processes, which at first 

 sight seemed utterly unrelated, from a cen- 

 tral point of view. This, in turn, has led 

 to the development of a mode of thought 

 which tends to correlate the findings in a 

 diversity of fields and on a variety of ob- 

 jects. For this field of scientific endeavor 

 Kluyver has coined the name "compara- 

 tive biochemistry," and already this has 

 proved fruitful in many cases. A few 

 examples will illustrate its value. 



It is well known that Knoop and Dakin 

 have developed the theory that in fat me- 

 tabolism the degradation of the fatty acid 

 proceeds by the so-called ^-oxidation 

 through which the carbon chain becomes 

 progressively shorter by 2 carbon atoms at 

 a time. In his general survey of this prob- 

 lem Knoop (1931) stated that the fate of 



7 ' ' This would mean that — apart from hydrolysis 

 and its reversion — the whole of biochemistry, the 

 complex of all biochemical changes brought about 

 by living cells, can be reduced to chains of volun- 

 tary primary reactions, each of which consists in a 

 coupled dehydrogenation and hydrogenation. 



Since these oxido-reduetion reactions differ in 

 detail, we can summarize the essence of biochem- 

 istry in the scheme: 



(I) AH + B^A + BH 

 (II) AH.B ^A.BH 



(III) AH.B -^A + BH 



(IV) AH + B ^ A.BH 



It mil be clear that, if we really accept this 

 hypothesis — and in my opinion quite a sufficient 

 number of arguments point to its correctness — it 

 must have an effect on our general outlook on 

 metabolic processes." (Kluyver, p. 91-92.) 



