Multiple carriers for dipeptide transport: carrier-mediated transport of glycyl-L-proline in renal BBMV.
To determine whether multiple carriers are responsible for luminal uptake of glycyl-L-proline (Gly-Pro) in the renal proximal tubule, transport of Gly-[3H]Pro was measured in brush-border membrane vesicles (BBMV). A Line-weaver-Burk analysis of Michaelis-Menten kinetics revealed the presence of two carriers: a lower affinity, higher capacity carrier (Km = 1.3 x 10(-2) M; Vmax = 4.6 x 10(-8) mol.mg-1.min-1) and a higher affinity, lower capacity carrier (Km = 2.7 x 10(-7) M; Vmax = 7.8 x 10(-13) mol.mg-1.min-1). The dipeptides Gly-Sar, beta Ala-His, and pyroGlu-His competitively inhibited the low-affinity carrier. No effect on the Km or Vmax of Gly-Pro transport in this range was seen in the presence of the dipeptides Gly-Gly or cycloHis-Pro. The high-affinity carrier exhibited a different inhibition spectrum. Competitive inhibition of Gly-Pro transport was demonstrated for the dipeptides Gly-Gly and Gly-Sar. However, none of the other peptides tested above altered Gly-Pro transport in the high-affinity range, including pyroGlu-His, which is transported by a high-affinity carrier. At both low (4 x 10(-8) M) and high (4 x 10(-3) M) concentrations, uptake of Gly-Pro was stimulated in the presence of an inwardly directed H+ gradient but was unaffected by the presence of an inward Na+ gradient. In addition, measurements in the presence of valinomycin and an outwardly directed K+ gradient strongly suggest that H(+)-stimulated uptake at both concentrations is electrogenic.(ABSTRACT TRUNCATED AT 250 WORDS)
Skopicki
H A
HA
Department of Physiology, University of Health Sciences/Chicago Medical School, Illinois 60064.
Fisher
K
K
Zikos
D
D
Bloch
R
R
Flouret
G
G
Peterson
D R
DR
D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D004151:Dipeptides / Q000378:metabolism*; D006868:Hydrolysis; D007668:Kidney / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D011817:Rabbits; D013997:Time Factors
D004151:Dipeptides; C015248:glycylproline