kluyver's contributions to microbiology and biochemistry 



of previous investigations in this field had clearly indicated that the 

 nature of the metabolic conversion is often strikingly dependent on 

 the conditions under which the organisms were grown. This led to the 

 fundamental problem in how far it would be possible to differentiate 

 between the influence of environmental conditions obtaining during 

 growth and affecting mainly the potentialities of the cells, and of 

 those existing during the later stages of a culture and causing a 

 particular cell type to produce either one or another metabolic 

 product. 



Early experiments on mould metabolism had generally been con- 

 ducted with growing cultures in stationary liquid media. Here the 

 environmental conditions are subject to continuous changes, owing to 

 the assimilation of various ingredients of the culture medium and to 

 the accumulation of metabolic products. This had made a reasonably 

 critical evaluation and interpretation of the results of such experiments 

 w r ell-nigh impossible. Besides, with such cultures it could not be as- 

 certained whether a particular product w r as derived directly from the 

 substrate provided, or might have originated by a very different, 

 round-about route. The reason for this is that growth implies the for- 

 mation of new r cell materials, including reserve products, so that the 

 latter, rather than the substrate itself, might be the direct precursors 

 of the metabolic products in question. The formation of kojic acid by 

 the mould, Aspergillus flavus, is a case in point. It is easy to envisage 

 its formation from glucose ; the closely similar constitution of the two 

 substances suggests that the conversion would consist in a partial 

 oxidation and dehydration of the sugar. But the same mould had also 

 been reported to produce kojic acid w r hen grown at the expense of 

 various other substrates, such as pentoses, erythritol, and glycerol; 

 and this is rather difficult to understand as the result of a direct de- 

 gradation because their constitution does not at all resemble that of the 

 product. It seemed therefore much more reasonable to assume that in 

 these cases the substrates are first converted into reserve materials that 

 subsequently can yield glucose, and that the kojic acid is actually 

 formed only from this substance. 



In order to test this hypothesis Kluyver and Perquin [1933b] pre- 

 pared a culture of Asp. flavus in the manner described in more detail 

 below, and exposed aliquots to solutions of glucose, fructose, galactose, 

 arabinose, xylose, mannitol, erythritol, and glycerol. Analysis of the 



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