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Abstract
The effects of colloidal bismuth subcitrate (CBS) on porcine pepsin have been studied
in vitro. CBS inhibited pepsin activity in a pH-dependent manner. CBS was not active
at pH 4.0 but inhibited pepsin activity at pH 1.0 (IC50: 2.3 +/- 0.09 mmol/l) and
pH 2.0 (IC50: 8.9 +/- 0.7 mmol/l). This inhibition was reversible. In the presence
of the sulfhydryl ligand mercaptoethanol, which prevents precipitation of CBS, the
inhibitory potency of CBS increased. CBS bound to both positively (Amberlite) and
negatively charged (Dowex) ion exchangers in a pH-dependent manner. With increasing
acidity, binding to Amberlite increased, whereas binding to Dowex decreased. From
these data we conclude that negatively charged bismuth salts derived from CBS bind
at pH 2.0 and 1.0 via an ionic interaction to positively charged groups of pepsin,
thereby inactivating the enzyme.