title: Use of membrane vesicles to estimate the numbers of system y+ and system L amino acid transporters in human erythrocytes.
abstract: We have used equilibrium values for L-leucine and L-lysine uptake by right-side-out vesicles to estimate the membrane abundance (sites/cell) of Na(+)-dependent amino acid transport systems L and y+ in human erythrocytes. All of the intravesicular space was accessible to L-leucine, as judged by comparisons with uridine uptake via the equilibrative nucleoside transporter (10(4) sites/cell). In contrast, only 28% of the total intravesicular space was accessible to L-lysine uptake via system y+. Since human erythrocyte membranes generate an average of approximately 1000 vesicles/cell, these data provide evidence that system L is a relatively high-abundance membrane transport protein in human erythrocytes, while system y+ is present in smaller amounts (approximately 300 copies/cell). Calculated turnover numbers for L-lysine transport by system y+ at 37 degrees C are 24 s-1 for zero-trans influx and 150 s-1 for equilibrium-exchange influx.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors.forename: C M
authors.initials: CM
authors.lastname: Tse
authors.forename: D A
authors.initials: DA
authors.lastname: Fincham
authors.forename: J C
authors.initials: JC
authors.lastname: Ellory
authors.forename: J D
authors.initials: JD
authors.lastname: Young
mesh_terms: D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000097:blood*; D004910:Erythrocyte Membrane / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000097:blood*; D008239:Lysine / Q000097:blood*; D013379:Substrate Specificity; D014529:Uridine / Q000097:blood / Q000494:pharmacology
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D002352:Carrier Proteins; D007930:Leucine; D008239:Lysine; D014529:Uridine