Abstract
1. From the cells of a strain of Lactobacillus casei, three kinds of lactic dehydrogenase were isolated. These are (i) a flavin-containing D-lactic dehydrogenase, (ii) a flavin-containing L-lactic dehydrognease and (iii) a DPN-linked D-lactic dehydrogenase. The former two were purified to almost homogeneous states.
2. These two enzyme showed, besides the difference in their substrate specificity, differences in their Km value, in their specificity towards electron acceptor and in their susceptivity towards atabrine. The prosthetic group of the D-enzyme was identified as FAD, while that of the L-enzyme was concluded to be some flavine nucleotide other than FAD.
3. Whereas the presence of a DPN-linked D-lactic dehydrogenase was confirmed beyond all doubt, no evidence whatsoever could be obtained for the existence of a DPN-linked L-enzyme. The absence of the latter enzyme was surprising in view of the fact that the bacterium used in the present study is a producer of L-lactic acid only.
4. The possible role of the flavin-containing L-lactic dehydrogenase in the L-lactic acid fermentation of this bacteria was discussed.
