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Abstract

Uptake of L-alanine and L-phenylalanine by purified bursh-border-membrane vesicles isolated from human small intestine was investigated by using a rapid-filtration technique. L-Alanine entered the same osmotically reactive space as D-glucose, indicating that transport into the vesicle rather than binding to the membranes was being observed. The uptake rate for L-alanine was higher in the presence of a Na⁺ gradient than in the presence of a K⁺ gradient. In the presence of a Na⁺ gradient, the lipophilic anion SCN⁺ caused an increase in L-alanine transport, whereas the nearly impermeant SO₄^2- anion decreased the uptake of L-alanine compared with its uptake in the presence of Cl^-. The uptake of L-phenylalanine into the brush-border-membrane vesicle was also stimulated by Na⁺. The results indicate co-transport of Na⁺ and neutral amino acids inthe human intestinal brush-border membrane.