AJP - Regulatory, Integrative and Comparative Physiology, Vol 259, Issue 6 1181-R1188, Copyright © 1990 by American Physiological Society
Lysine transport by brush-border membrane vesicles of eel intestine: interaction with neutral amino acids
S. Vilella, G. A. Ahearn, G. Cassano, M. Maffia and C. Storelli
Laboratorio di Fisiologia, Universita di Lecce, Italy.
L-[3H]lysine uptake was measured in brush-border membrane vesicles prepared
from intestinal mucosa of the European eel Anguilla anguilla. Lysine uptake
occurred via 1) a nonsaturable component with an apparent diffusional
permeability (P) of 0.58 microliter.mg protein-1.min-1,2) a Na-dependent
transport system [half-saturation constant (Kapp) 0.16 mM, maximal
transport rate (Jmax) 3.57 nmol.mg protein-1.min-1]; 3) a Na-independent
transport system (Kapp 0.17 mM, Jmax 2.77 nmol.mg protein-1.min-1). Both
carrier-mediated processes were accelerated by the presence of an
intravesicular negative membrane potential. Hill analysis of L-lysine
influx, over a wide range of external Na concentrations, resulted in a Hill
coefficient (n) of approximately 2, suggesting that two or more Na ions may
be associated with amino acid transport. The inhibition of lysine uptake by
other amino acids was studied. Na-dependent lysine uptake was competitively
inhibited by proline [inhibitory constant (Ki) approximately 2 mM] and may
occur by a system specific for cationic amino acids. Na-independent lysine
uptake was competitively inhibited by alanine (Ki approximately 1 mM) and
may occur by a classic L system.
