Abstract
Although diacetylthiamine (DAT) , purified by repeated recrystalization, showed no growth-stimulating activity for L. fermenti in the broth without cysteine, it was shown to be slightly growth-stimulating in 10^<-5>-10^<-4>×1/4M but inhibitory in the higher concentration in the broth with cysteine. DAT, in the broth containing thiamine-HCI (10^<-6>×l/4M) was proved to be inhibitory to growth both in presence and absence of cysteine ; 50% inhibition index is 250 (with cysteine) or 500(without cysteine) . As both cysteine and histidine stimulate hydrolysis of DAT, increased addition of cysteine to the broth(176mg%) resulted in growth-stimulation of L, fermerti but increased addition of histidine gave no stimulation for growth, because of slow hydrolysis of DAT by histidine (Fig. 5).
