SUMMARY: Pseudomonas strains, capable of utilizing as carbon sources one or more isomers of tartaric acid, were isolated from soil by specific elective culture methods. Most strains were markedly stereospecific. utilizing only the isomer or isomers upon which they had developed during the elective cultivation. Enzymic study showed that the commonest mechanism for the dissimilation of the tartaric acids by this group of strains is dehydration to oxaloacetic acid, through the action of stereo-specific dehydrases. The attack on the tartaric acids is strictly inducible, and in many strains the induced state is rapidly lost in the absence of the substrate-inducer. Enzymic assay showed that such loss of induction cannot be accounted for by loss of the specific dehydrase, which is often present in large quantities in organisms which have become incapable of attacking the substrate. This indicates that the metabolism of the tartaric acids requires specific inducible transport systems for bringing the tartaric acids into the cell, in addition to the specific, inducible dehydrases. The existence of such transport systems is further indicated by the fact that the inhibitory interactions between the isomers of tartaric acid, demonstrable with the cell-free dehydrase preparation, do not exist .


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