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Proline transport by brush-border membrane vesicles of lobster antennal glands
Ist Teil von
American journal of physiology. Renal physiology, 1990-02, Vol.258 (2), p.311-F320
Ort / Verlag
United States
Erscheinungsjahr
1990
Quelle
MEDLINE
Beschreibungen/Notizen
R. D. Behnke, R. K. Wong, S. M. Huse, S. J. Reshkin and G. A. Ahearn
Department of Zoology, University of Hawaii, Manoa, Honolulu 96822.
Purified brush-border membrane vesicles (BBMV) of lobster antennal gland
labyrinth and bladder were separately formed by a magnesium precipitation
technique. L-[3H]proline uptake was stimulated by a transmembrane NaCl
gradient [outside (o) greater than inside (i)] to a greater extent in BBMV
from labyrinth than those from the bladder. Detailed study of the labyrinth
proline-transport processes revealed a specific dependence on NaCl, with
negligible stimulatory effects by NaSCN, Na-gluconate, or KCl. A
transmembrane proton gradient (o greater than i) was without stimulatory
effect on proline transport. A transmembrane potential difference alone, in
the presence of equilibrated NaCl and L-[3H]proline, led to net influx of
the labeled amino acid, suggesting that the uptake process was electrogenic
and capable of bringing about the net transfer of positive charge to the
vesicle interior. Although a transmembrane Na gradient alone, in the
presence of equilibrated Cl and L-[3H]proline, was able to bring about the
net influx of the amino acid, a transmembrane Cl gradient alone under Na-
and L-[3H]proline-equilibrated conditions was not, suggesting that only the
Na gradient could energize the carrier process through cotransport, while
the anion served an essential activating role. Proline influx by these
vesicles occurred by the combination of at least one saturable
Michaelis-Menten carrier system (apparent Kt = 0.37 mM; apparent JM = 1.19
nmol.mg protein-1.10 s-1) and apparent diffusion (P = 0.33 nmol.mg
protein-1.10 s-1.mM-1). Static head analysis of the transport process
suggested a cotransport stoichiometry of 2 Na:1 proline with essential
activation by Cl ion.