L-LYSINE TRANSPORT IN CHICKEN JEJUNAL BRUSH-BORDER MEMBRANE-VESICLES

The properties of L-lysine transport in chicken jejunum have been stud ied in brush border membrane vesicles isolated from 6-wk-old birds. L- lysine uptake was found to occur within an osmotically active space wi th significant binding to the membrane. The vesicles can accumulate L- lysine against a concentration gradient, by a membrane potential-sensi tive mechanism. The kinetics of L-lysine transport were described by t wo saturable processes: first, a high affinity-transport system (K-mA = 2.4 +/- 0.7 mu mol/L)) which recognizes cationic and also neutral am ino acids with similar affinity in the presence or absence of Na+ (L-m ethionine inhibition constant K-iA, NaSCN = 21.0 +/- 8.7 mu mol/L and KSCN = 55.0 +/- 8.4 mu mol/L); second, a low-affinity transport mechan ism (K-mB = 164.0 +/- 13.0 mu mol/L) which also recognizes neutral ami no acids. This latter system shows a higher affinity in the presence o f Na+ (K-iB for L-methionine, NaSCN = 1.7 +/- 0.3 and KSCN = 3.4 +/- 0 .9 mmol/L). L-lysine influx was significantly reduced with N-ethylmale imide (0.5 mmol/L) treatment. Accelerative exchange of extravesicular labeled L-lysine was demonstrated in vesicles preloaded with 1 mmol/L L-lysine, L-arginine or L-methionine. Results support the view that L- lysine is transported in the chicken jejunum by two transport systems, A and B, with properties similar to those described for systems b(0,) and y(+), respectively.