Adaptive enzymes in the estimation of gluconate D-arabinose, and D-ribose.

The small amount of carbohydrate available in our recent studies (1) of pentose formation from 6-phosphogluconic .acid has led us to examine microbiological analytical tools. In earlier studies on uranic acid metabolism in an Escherichia coli strain (2), it had become clear that the adaptive synthesis of new enzyme systems in response to the presence of specific substrates is extraordinarily specific. Cells adapted to uranic acids were incapable of fermenting n-ribose, n-arabinose, or n-xylose. Cells adapted to any one of these pentoses were incapable of fermenting the other two. Furthermore, the adaptive method provided a true control for the microbiological analysis of a mixture of sugars, since the strains examined are capable of using glucose and certain other sugars non-adaptively (i.e. with constitutive enzymes), whereas the adapted strain can utilize these substrates plus the new substrate. Therefore, non-adapted cells could be used to exhaust the substrate of fermentable material, with the exception of the substance to be determined on addition of the adapted cells. Gluconate, n-arabinose, and ribose were susceptible of analysis by this method with E. coli. Of additional interest is the analysis of the pathway of gluconate metabolism provided by these studies. Since cells adapted to gluconate were unable to utilize 2-ketogluconate, n-arabinose, or n-arabonate, we may conclude as a function of the postulates of simultaneous adaptation (3) that these substances as such were not intermediates in the degradation of gluconate.