BIOGRAPHICAL MEMORANDA 



relation between breakdown and synthesis by considering the former 

 as the means whereby are supplied the energetically elevated building 

 blocks from which the synthetic reactions can proceed spontaneously. 



If we compare this concept with present-day knowledge it will be 

 clear that there has not been a fundamental change in outlook. To be 

 sure, our understanding of the intimate details of biochemical mecha- 

 nisms has been immensely increased and broadened. We no longer 

 think in terms of acetaldehyde as a key intermediate product, for 

 example. Nonetheless, the mere substitution of 'acetyl-coenzyme A' 

 for this substance is all that is required to show that the latest ideas 

 on the mechanism of fatty acid synthesis are virtually identical with 

 those that Kluyver had suggested more than 25 years ago. If we fur- 

 thermore remember that acetyl-coenzyme A formation is currently 

 interpreted as the direct result of catabolic conversions, it is evident 

 that we have achieved a much more detailed, but not a fundamentally 

 different comprehension of the mechanism of synthetic processes. 



This concept of assimilation and dissimilation as inextricably linked 

 aspects of what Kluyver called 'metabolism one and indivisible' could 

 have been experimentally tested, for example by determining the 

 amount of growth (assimilation) of particular organisms in media with 

 various substrates, inclusive of those which, as intermediate products, 

 were presumed to be used as the direct participants in the synthetic 

 processes. But it was generally believed that the amount of cell mater- 

 ial formed in simple media is very small compared to the quantity 

 of substrate used, which made it unlikely that accurate experiments 

 of this sort would be feasible. Another deterrent to such studies was 

 the high volatility and toxicity of acetaldehyde, one of the most 

 crucial amongst the intermediate products. 



This situation was changed when Barker [1936], in studies on the 

 oxidation of small amounts of substrates by resting cell suspensions of 

 Prototheca zopfii, found that the quantities of oxygen consumed and 

 carbon dioxide produced were far short of those required for complete 

 oxidation of the substrates, and interpreted these results, as well as 

 earlier ones obtained by Cook and Stephenson [1928] in similar stud- 

 ies with B. coli, to mean that the oxidation was accompanied by an 

 assimilation of considerable magnitude, sometimes amounting to more 

 than half of the substrate carbon. The significance of this phenomenon 

 did not escape Kluyver, and soon thereafter his collaborator, Giesber- 



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