Susceptibility of Kintoki bean lectin to digestive enzymes in vitro and its behavior in the digestive organs of mouse in vivo.

The enzymatic digestion of a Kintoki bean lectin in vitro resulted in neither the extensive hydrolysis nor complete inactivation of the lectin. The majority of [3H]lectin administered to mice by stomach-intubation was found in the digestive tract at levels of 88.7%, 99.4%, 99.5% and 78.6%, after 0.5, 2, 5 and 24h of intubation, respectively. Twenty to forty percent of the administered radioactivity was found combined with the mucosa of the small intestine. After 24 h of intubation, part of the radioactivity was found in the feces. The recovery test of hemagglutinating activity and the molecular weight determination of the lectin administered to and recovered from mice revealed that more than 70% of the radioactivity detected in the digestive tract represented intact lectin. Therefore, it was concluded that most of the Kintoki bean lectin survived its passage through the gastrointestinal tract. The lectin-binding sites in the intestinal mucosa were traced with fluorescence microscopy using the lectin conjugated with fluorescein isothiocyanate. The fluorescent sites were found located at the top and upper sites of the villi, but not at the crypt.