抄録
A large amount of O-acetyl-L-homoserine (OAH) was found to be produced by trifluoromethionine-resistant mutants derived from Corynebacterium glutamicum ESLR-146 (Thr-, ethionineR, selenomethionineR) and ETzR-606 (Thr-, ethionineR, 1, 2, 4-triazoleR) by mutational treatment with ethyl methanesulfonate. Some cultural conditions for OAH production were examined with one of the mutants, ESLFR-736, which was derived from ESLR-146. Addition of L-methionine or L-serine decreased OAR production. Optimal level of L-threonine, a growth factor in ESLFR-736, for OAH production was about 200μg/ml, and further addition of excess L-threonine repressed OAH production. Corn steep liquor (CSL) and yeast extract added simultaneously enhanced OAH production to a great extent. Thus, the amount of OAH production reached to a level of 10.5mg/ml with a medium containing 10% glucose and 0.01% of both CSL and yeast extract after 2 days incubation.
Cell-free extract of C. glutamicum catalyzed the formation of OAH from acetyl CoA and L-homoserine, while a corresponding reaction with succinyl CoA was hardly detected. These observations indicate that OAH but not O-succinyl-L-homoserine is an intermediate of L-methionine biosynthesis in C. glutamicum.
The regulation of homoserine-O-transacetylase was examined in a methionine requiring mutant of C. glutamicum. The enzyme activity was not inhibited by L-methionine, S-adenosylmethionine and S-adenosylhomocysteine, separately or in combination. The synthesis of homoserine-O-transacetylase was strongly repressed by L-methionine. The enzyme level in an OAH producer, ESLFR-736, increased to about 2-fold of that in ESLR-146, the parental strain.
