Binding of navy bean (Phaseolus vulgaris) lectin to the intestinal cells of the rat and its effect on the absorption of glucose.

The main objectives of this investigation were to study the binding of a lectin from navy beans with the epithelial cells of the rat intestine and to assess the effect of such binding on the ability of the intestine to absorb glucose. A Scatchard plot, based on the binding of 125I-labeled lectin to isolated intestinal epithelial cells, was used to calculate an association constant (Ka) of 15 x 10(6)M-1 and the number of binding sites per cell, 12 x 10(6). Metabolic studies were conducted over a period of 5 d on groups of rats fed raw or autoclaved navy bean flour and casein with or without the purified lectin. Growth, protein digestibility, biological value and net protein utilization were significantly lower in animals that had been fed raw navy bean flour or casein plus lectin than in control groups fed diets containing autoclaved navy bean flour or casein alone. Vascular perfusion was used to measure the rate of uptake of glucose by the intestines of rats that had received the various dietary treatments. The rate of absorption of [14C]glucose by intestines from rats fed raw navy bean flour or casein plus lectin was approximately one-half that of their counterparts fed the autoclaved flour or casein alone. These results provide evidence that the lectin, by virtue of its interference with intestinal absorption, is responsible, at least in part, for the nutritional inferiority of raw navy beans.

Starch blockers: a potential source of trypsin inhibitors and lectins.

Highly variable levels of amylase, amylase inhibitor, trypsin inhibitor, and lectin activities were found in 10 randomly selected brands of starch blockers. This variability was attributed to the crude nature of the legume protein concentrate used in the formulation of these tablets. In addition to the possible risk to health associated with their trypsin inhibitor and lectin content, the levels of endogenous amylase activity present in such tablets may serve to counteract their alleged effectiveness as inhibitors of starch digestion.