Abstract
The mechanism of isoleucine formation from D-threonine in isoleucine fermentation was studied with special reference to the rôle of D-threonine dehydrase.
1. Optimum condition for the formation of D-threonine dehydrase coincides with that for isoleucine fermentation.
2. D-Threonine dehydrase was inducibly formed by D-threonine.
3. DL-Allothreonine dehydrase activity was not found in the media containing any threonine isomer.
4. Although L-threonine dehydrase was markedly inhibited by lower concentration of L-isoleucine, D-threonine dehydrase activity was not inhibited by the presence of isoleucine at such a concentration as produced during the fermentation.
5. Presence of L-threonine resulted in the repression and inhibition of D-threonine dehydrase.
6. Although the difference in the iso-leucine forming activities from α-ketobutyric acid between the cells grown in the media containing L- and D-threonines was not so large, the latter activity was slightly better than the former.
From these facts, it was confirmed that D-threonine dehydrase plays an important rôle for this isoleucine fermentation using D-threonine, and that specific isoleucine accumulation observed only in the medium containing D-form among the threonine isomers is also explained by the difference of the threonine dehydrase activities.
The author wishes to thank President S. Akabori, Prof. H. Kikkawa and Assist. Prof. Y. Izumi, Osaka University, for their interest and helpful advice throughout this work. I am also greatly indebted to Mr. T. Hirabayashi, Representative Director of the Tanabe Seiyaku Co. Ltd., Dr. M. Fujisawa, Research Executive, Dr. N. Sugimoto, Director of Osaka Research Laboratory for continued encouragement and assistance.
