Identification of a new transport system (y+L) in human erythrocytes that recognizes lysine and leucine with high affinity.

Abstract

SUMMARY1. The effect of neutral amino acids on the transport of L-lysine across the human erythrocyte membrane was studied.2. All neutral amino acids tested (range 0 3-5 mM) inhibit the influx of L-[14C]lysine (1 /tM). The inhibition pattern is biphasic, and tends to reach a maximum at approximately 50 % of the original flux. The concentrations that give 25 % inhibition are (mM):L-lysine and Larginine completely inhibit the rate at the highest concentration.3. These results can be explained by assuming that L-lysine transport occurs through two independent transporters that differ in their affinity for neutral amino acids. A detailed kinetic analysis of the effect of L-leucine on L-lysine entry is consistent with this hypothesis.4. Using a new experimental strategy, the substrate and inhibitor transport parameters for the two systems were determined. The half-saturation constants for lysine (±S.E.M.) are found to be: KmA, 0-014+0-002 mm and KmB, 0 112+0-017 mM. The maximum rates differ by a factor of 8-2 (VmaXB/VmaxA). The leucine inhibition constants are: KiA, 0-022 + 0-003 mm and KiB, 30-36+7-9 mm. If the sodium in the incubation medium is replaced by potassium, the apparent affinity for leucine (1/KiA) is reduced approximately 30-fold.5. The maximum inhibition caused by leucine decreases as the lysine concentration is raised, showing that leucine acts upon the higher affinity system. 6. When added to the trans side, L-leucine, L-phenylalanine and L-isoleucine do not cause inhibition, but stimulate the flux by approximately 30%. This indicates that these analogues are also transported.7. In conclusion, in the concentration range 1-100 ,tM, lysine crosses the red cell membrane through two distinct transport systems, one of which recognizes both neutral and cationic amino acids with high affinity.MS 9679

Cloning and Expression of a Plasma Membrane Cystine/Glutamate Exchange Transporter Composed of Two Distinct Proteins

“…System L-and y ϩ L-like transport activity expressed in oocytes seem to show an obligatory exchange, although the molar ratio of exchange is not determined (15,16,20). System L and y ϩ L naturally expressed in cells show marked transstimulation (1,21), that is, the substrate amino acids in one side of the membrane stimulate the exodus of the substrate amino acids from the opposite side of the membrane. However, it has not been proved yet that the naturally occurring system L or y ϩ L is locked into exchange, and the possibility that the obligatory exchange mechanism of an L-or y ϩ L-like system is an oocyte artifact has not been ruled out.…”

Accumulation of the endogenous L‐arginine analogue NG‐monomethyl‐L‐arginine in human end‐stage renal failure patients on regular haemodialysis

“…In red blood cells and certain other types of mammalian cells L-arginine transport is mediated by two separate saturable facilitated diffusion transporters and a linear component that does not saturate and represents uptake by other systems with low affinity for L-arginine plus simple diffusion (Deves, Chavez & Boyd, 1992). These have been defined as y+ (mcat-1), a high capacity cationic amino acid transporter, with a Km of around 0 06 mm, and y+L, a low capacity, higher affinity system with a Km of 0 001 mm, which also has an affinity for sodium and neutral amino acids.…”

The rBAT Gene Is Responsible for L-Cystine Uptake via the bo,+-like Amino Acid Transport System in a “Renal Proximal Tubular” Cell Line (OK Cells)

“…This suggests that part ([mteq]30%) of L-arginine and L-leucine uptake is due to transport activities resembling systems y ϩ and L, respectively. On the other hand, interaction of L-leucine with sodium-independent L-arginine uptake suggests system b 0,ϩ -like or system y ϩ L transport activities (27,38,39). Inhibition of 50 M Larginine uptake by varying concentrations of L-leucine (100 M to 10 mM) was identical in the absence and in the presence of sodium (data not shown).…”