Etude des mutants chlorate-résistants chez Escherichia Coli K12 III. Mise en évidence et étude de l'activité chlorate-réductase c des mutants chl C −

Abstract

Analysis of the biochemical properties of the mutant chl C − of E. coli K12 has given evidence for a chlorate reductase activity independent of nitrate reductase A which is induced by KNO 3 in this bacterium. This particulate enzyme is not sensitive to NaN 3 or KNC, its K m with respect chlorate is 2.5·10 −4 M. Reduced pyridine nucleotides cannot serve as electron donors. FMN ( K m = 0.19 mM) and riboflavine ( K m = 0.62 mM) are less effective electron donors than benzyl viologen ( K m = 0.6·10 −4 M). This chlorate reductase activity shows a number of analogies with the chlorate reductase C found in other Enterobacteriaceae. Repressed by NO 3− and ClO 3− in the mutant chl C −, it is absent in the pleiotropic mutants chl A − and chl B − of Escherichia coli K12 regardless of the culture conditions. It is probable that this enzyme acts as an electron barrier, integral to the multienzyme system that produces gaseous H 2 during the fermentation of glucose. Thus, the pleiotropic mutation of chlorate-resistant mutants of E. coli K12 affects three different enzymatic activities: formate dehydrogenase, nitrate reductase, and chlorate reductase.