Transport of L-lysine by rat intestinal brush border membrane vesicles

Brush border membranes were isolated from rat jejunum by a divalent cation precipitation method. 3H-L-Lysine uptake was measured by a rapid filtration technique. Uptake after prolonged incubation periods was osmotically insensitive and represented almost exclusively binding to the vesicles. Extrapolating initial linear uptake to a zero incubation time indicated no binding of the amino acid to the external membrane surface. Sodium did not significantly alter the initial uptake rate. L-Lysine transport represents a carrier mediated uptake in the presence and absence of sodium as indicated by the transstimulation experiments. The transport mechanism operates stereospecifically and is inhibited by other basic amino acids and L-leucine and L-phenylalanine. Saturation experiments result in a Km of 0.26 mmoles/l and a Vmax of 272 pmoles/mg protein/10s. Inside negative anion diffusion potentials and inside negative potassium diffusion potentials (valinomycin) were unable to increase the transport rate. Transmembrane pH-gradients were also unable to alter transport.