NEGATIVE FEED-BACK CONTROL CAUSED BY THREONINE AND METHIONINE IN L-HOMOSERINE FERMENTATION

摘要

Fermentative production of L-homoserine was achieved by using a threonine requiring mutant of Micrococcus glutamicus. This strain produced a large quantity of L-homoserine as well as L-lysine in the culture broths if it was cultivated under appropriate conditions.During the studies on fermentative production of L-homoserine, it was found that L-threonine concentration affected the formation of L-homoserine and L-lysine to a great extent. Maximum productions of L-homoserine and L-lysine were attained when L-threonine concentrations were 400μg/ml and 300 μg/ml, respectively. And an excess amount of threonine caused a sharp decrease in both amino acid productions. The effects of various amino acids on this fermentation were also examined. As the results, two "negative feed-back control" phenomena caused by threonine and methionine were observed.Further investigations using intact cell suspension revealed the mode of action of the two amino acids in the "negative feed-back" mechanisms. Experimental results showed that threonine inhibited a certain enzyme activity involved in the biosynthetic path of homoserine, and methionine repressed the formation of a certain enzyme on the same path.Based on these experimental results the sites of these "negative feedback" mechanisms were discussed.