Abstract
When papain was incubated with thiamine propyldisulfide (TPD) in increasing concentrations, its enzymatic activity was inhibited proportionally to the thiamine released from TPD. Determination of thiol radicals of TPD-ihibited papain by p-(bis-nitrophenyl) disulfide (PNPD) also indicated decrease of PNPD-values in correspondence with enzymatic activity of the papain. The activity of TPD-inhibited papain, when incubated with ICH_2COOH, was completely destroyed but the thiol radicals detected by PNPD were always demonstrated to the extent of 45-50% of the papain-SH value. When papain was incubated with ICH_2COOH and TPD, thiamine was hardly released and thiol radicals detected by PNPD were also demonstrated to 47% of the papain-SH. When papain was denatured by urea in increasing concentrations, the thiamine released from TPD in its incubation with TPD, was proportional to the enzymatic activity of urea-denatured papain, while the radicals detected by PNPD were always demonstrated. That the thiamine released from TPD in the incubation of papain with TPD was shown to be a good index of the enzymatic activity.
