Abstract
When pure YADH (yeast alcohol dehydrogenase) was incubated with TPD (thiamine propyldisulfide) at the pH ranges between 5.5 and 9.5,the activity of YADH was decreased and thiamine was released from TPD. The amounts of thiamine from TPD were higher at the alkaline ranges of pH but inhibition of YADH activity was observed to the same extent both at pH 5.5 and 8.6,as shown in Fig.1 and 2. The thiol-radicals of YADH, blocked by TPD at pH 5.5,seemed to be responsible for its enzymatic activity. The thiamine, converted from TPD at pH 5.5 by YADH can be interpreted to be 'active thiols' which will be calculated as 5.5 moles per mole of YADH. This thiol value is much smaller than the values, calculated by PCMB or PNPD method. Thiamine, however, can be released from TPD, even with inert YADH, denatured by heat, acid, alkali or urea treatments; the amounts were corresponding to the values measured by PNPD method.
