ISSN:
1432-072X
Keywords:
Archaebacteria
;
Extreme halophiles
;
Halobacterium vallismortis
;
Phenylalanine biosynthesis
;
Regulatory mutants
;
Prephenate dehydratase
;
Metabolic interlock
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The focal point of phenylalanine biosynthesis is a dehydratase reaction which in different organisms may be prephenate dehydratase, arogenate dehydratase, or cyclohexadienyl dehydratase. Gram-positive, Gram-negative, and cyanobacterial divisions of the eubacterial kingdom exhibit different dehydratase patterns. A new extremehalophile isolate, which grows on defined medium and is tentatively designated as Halobacterium vallismortis CH-1, possesses the interlock type of prephenate dehydratase present in Gram-positive bacteria. In addition to the conventional sensitivity to feedback inhibition by l-phenylalanine, the phenomenon of metabolic interlock was exemplified by the sensitivity of prephenate dehydratase to allosteric effects produced by extra-pathway (remote) effectors. Thus, l-tryptophan inhibited activity while l-tyrosine, l-methionine, l-leucine, and l-isoleucine activated the enzyme. l-Isoleucine and l-phenylalanine were effective at μM levels; other effectors operated at mM levels. A regulatory mutant selected for resistance to growth inhibition caused by β-2-thienylalanine possessed an altered prephenate dehydratase in which a phenomenon of disproportionately low activity at low enzyme concentration was abolished. Inhibition by l-tryptophan was also lost, and activation by allosteric activators was diminished. Not only was sensitivity to feedback inhibition by l-phenylalanine lost, but the mutant enzyme was now activated by this amino acid (a mutation type previously observed in Bacillus subtilis). It remains to be seen whether this type of prephenate dehydratase will prove to be characteristic of all archaebacteria or of some archaebacterial subgroup cluster.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00411657
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