Mechanism of l -Glutamine Production by an l -Glutamine-Producing Mutant of Flavobacterium rigense

Abstract

Properties of some enzymes involved in l -glutamine biosynthesis in an l -glutamine-producing mutant of Flavobacterium rigense were examined. Glutamate-oxaloacetate transaminase in the mutant was nearly at the same level as that in the parent strain and was the most active among the enzymes participating in glutamate biosynthesis from α-ketoglutarate. Glutamine synthetase formation in the mutant was enhanced by increasing the concentration of (NH 4 ) 2 -fumarate in the medium, but the activity of this enzyme in the parent strain was very low, and its formation was not influenced by the concentration of (NH 4 ) 2 -fumarate. Glutaminase formation by both strains was similar and was not influenced by the levels of (NH 4 ) 2 -fumarate. Glutaminase activity of the mutant was inhibited by ammonia and fumarate. Intracellular amino acids and extracellular free amino acids in the mutant were compared with those of the parent strain. It seems reasonable to conclude that l -glutamine leaks out specifically through the cell membrane of strain 703 and that this specific excretion of l -glutamine probably allows a continuous conversion of l -glutamate to l -glutamine inside the cell.