Abstract
As to the mechanism of the action of ethylthiamine, Mano and Kaziro in our laboratory reported the inhibitory effect of this thiamine analogue on the thiaminokinase from animal tissue and yeast, respectively. However, it is generally accepted that ethylthiamine, when fed to animals, shows the similar vitamin activity as thiamine. To solve the apparent controversy, the author carried out following experiments. First, ethylthiamine was fed to rats and the growth of the rats was compared to that of rats administered with thiamine. Then, the amount of thiamine and the activity of cocarboxylase in the liver of these animals were determined. The results of the experiments showed, as described previously by others, that ethylthiamine had almost the same degree of growth effect as thiamine. But, it was also found that the livers of the animals fed with ethylthiamine contained very small amount of cocarboxylase as determined manometrically, in spite of the fact that the livers contained large amount of bound form of thiamine as determined by the thiochrome method. In the animals fed with thiamine, these discrepancies were not observed. The liver extracts obtained from the animals fed with large amount of ethylthiamine were treated with Taka-diastase, and chromatographed on paper. An intensive thiochrome reaction-positive spot was detected on the paper chromatogram, and this spot had just the same Rf value as ethylthiamine. From these results obtained, it was presumed that ethylthiamine was converted to its bound form, probably ethylthiamine pyrophosphate, and the latter showed the low cocarboxylase activity for yeast carboxylase. The so-called Ochoa's effect of ethylthiamine and the other thiamine analogues was also studied using etiozymase and partially purified apocarboxylase from bakers' yeast, and it was observed that ethylthiamine has a distinct Ochoa's effect, thouth a little weaker than thiamine.
