Abstract
Several enzymes involved in the L-threonine and L-lysine biosynthesis in gram-negative obligate methylotrophs, Methylobacillus glycogenes ATCC 21276 and ATCC 21371, were characterized. The activities of aspartokinases were inhibited by L-threonine or L-lysine. The homoserine dehydrogenases were inhibited by L-threonine or L-phenylalanine. The dihydrodipicolinate synthase activities were inhibited by L-lysine. No activity of meso-α, ε-dihydrodipicolinate dehydrogenase, the by-path enzyme of L-lysine biosynthesis, was detected. The biosynthetic enzymes in L-threonine-producing and L-lysine-producing mutants of M. glycogenes were also characterized. The aspartokinases of all the mutants were insensitive to inhibition by L-threonine, and some were also insensitive to inhibition by L-lysine. The homoserine dehydrogenases of the mutants had the wild type-profiles. The dihydrodipicolinate synthase of the L-lysine-producing mutant was partially desensitized to inhibition by L-lysine.
