Na-dependent L-proline transport by eel intestinal brush-border membrane vesicles.

L-[3H]proline uptake by brush-border membrane vesicles prepared from intestinal mucosa of the European eel, Anguilla anguilla, was stimulated by a transmembrane Na gradient (out greater than in). Kinetic analysis of L-proline influx, under short-circuited membrane potential conditions, indicated the presence of an apparent single Na-dependent carrier process (Kapp = 0.23 +/- 0.04 mM and Jmax = 7.96 +/- 0.87 nmol.mg protein-1.min-1) and a nonsaturable transfer component with an apparent diffusional permeability (P) of 1.53 +/- 0.35 microliter.mg protein-1.min-1. An imposed transmembrane potential (inside negative) increased apparent L-proline binding affinity (lowered Kapp) without appreciably altering maximal amino acid influx (Jmax). Hill analysis of L-proline influx over a wide range of external Na concentrations indicated a 1:1 stoichiometry for Na-proline cotransport. Use of amino acid inhibitors of L-proline influx suggested that L-proline transfer may occur by either a classical Na-dependent A System with a wide substrate specificity or by the combination of Na-dependent PHE (phenylalanine preferring) and IMINO (proline, alpha-methylaminoisobutyric acid preferring) Systems.