Comparative allostery of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthetase as an indicator of taxonomic relatedness in pseudomonad genera

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Abstract
An analysis of the enzymological patterning of L-tyrosine biosynthesis distinguished 5 taxonomic groupings among species currently named Pseudomonas, Xanthomonas or Alcaligenes (Byng et al.). These groupings paralleled with striking consistency those previously defined by rRNA-DNA homology relationships. The comparative allostery of 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthetase is a useful indicator of taxonomic relationship at about the level of genus. The comparative allostery of DAHP synthetase was evaluated in relationship to data availabe from the same pseudomonad species previously studied. Species of Xanthomonas and some named species of Pseudomonas, e.g., P. maltophilia, were unmistakably recognized as belonging to group V, having a DAHP synthetase sensitive to sequential feedback inhibition by chorismate. This control pattern is thus far unique to group V pseudomonads among microorganisms. Group V organisms were also unique in their possession of DAHP synthetase enzymes that were unstimulated by divalent cations. Group IV pseudomonads (P. diminuta) were readily distinguished by the retro-tryptophan pattern of control for DAHP synthetase. Activity for DAHP synthetase was not always recovered in group IV species, e.g., P. vesicularis. The remaining 3 groups exhibited overlapping patterns of DAHP synthetase sensitivty to L-phenylalanine and L-tyrosine. Individual species cannot be reliably keyed to group I, II or III without other data. Each group overall exhibited a different trend of relative sensitivity to L-tyrosine and L-phenylalanine. Although enzymological patterning of L-tyrosine biosynthesis alone can be used to separate the 5 pseudomonad groups, the independent assay of DAHP synthetase control pattern can be used to confirm assignments. The latter approach is the easiest and most definitive method for recognition of group V (and often of group IV) species.