N-ethylmaleimide discriminates between two lysine transport systems in human erythrocytes.

摘要: 1. The sulfhydryl reagent N-ethylmaleimide (NEM) was shown to inactivate the low affinity lysine transporter in human erythrocytes (system y+) without affecting high y+L). 2. Pre-treatment of cells with NEM reduced rate entry L-[14C]lysine (1 microM) by approximately 50% (maximum effect). 3. (0.2 mM) inhibited NEM-sensitive component flux mono-exponential kinetics. inactivation constant (k, +/- S.E.M.) 0.53 0.027 min-1 (25 degrees C). substrate did not protect against inactivation. 4. Lysine self-inhibition experiments revealed two transport systems untreated (half-saturation constants Km; S.E.M.), 12.0 1.7 microM and 109 15.6 only one system NEM-treated (Km 9.5 0.67 microM), indicating that inactivates y+. 5. NEM-insensitive influx y+L) unlabelled neutral amino acids. inhibition for L-leucine sodium medium (Ki 10.7 0.72 (37 also strongly L-methionine, L-glutamine less L-phenylalanine L-serine. N-methyl-L-leucine, L-proline 2-amino-2-norbornane-carboxylic acid, a bicyclic analogue leucine, exert significant effect. 6. through y+L occurred at same Na+, K+ or Li+ binding unaffected Na+ replacement. 7. interaction acids dependent on cation present medium. leucine glutamine increased 90- 60-fold respectively when replaced K+. be very good substitute Na+.