[Regulation of the activity and synthesis of 3-deoxy-D-arabinoheptuloso-7-phosphate synthase in the obligate methylotroph Methylobacillus flagellatum KT]

Abstract

The activity of the first enzyme of aromatic path 3-deoxy-D-arabino-heptuloso-7-phosphate-synthase (DAHP-synthase) is regulated by retro-inhibition and is a subject of repression. Analysis of partially purified preparations of the enzyme has revealed three isoenzymes: DAHP-synthase-Tyr, DAHP-synthase-Trp and DAHP-synthase-Phe, each of them being regulated by a corresponding amino acid. DAHP-synthase-Phe is a dominant isoenzyme presenting 70% of the enzyme activity, 30% inhibition of which is possible by 7.0 mkM of phenylalanine. DAHP-synthase-Tyr and DAHP-synthase-Trp are minor isoenzymes (sharing 15% of enzyme activity each) and are controlled by tyrosine and tryptophane correspondingly. 50% of inhibition of activity is possible by adding 0.7 and 0.8 mkM of corresponding amino acid. Regulation of the enzyme synthesis was studied in the Trp-, Phe- and Tyr- mutants. The enzyme activity was registered under the conditions of limiting and surplus of each aromatic amino acid. The synthesis of DAHP-synthase in M. flagellatum KT is repressed by tryptophane and tyrosine decreasing the synthesis 18.8 and 15.6 fold.