Title
Transport of ascorbate into plasma membrane vesicles of **Phaseolus vulgaris** L. Transport of ascorbate into plasma membrane vesicles of **Phaseolus vulgaris** L.
Author
Faculty/Department
Faculty of Sciences. Biology
Publication type
article
Publication
Wien ,
Subject
Biology
Human medicine
Source (journal)
Protoplasma. - Wien
Volume/pages
194(1996) :3/4 , p. 177-185
ISSN
0033-183X
ISI
A1996VV75900006
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
Incubation of bean hook plasma membrane vesicles in the presence of L-[C-14]ascorbate (ASC) resulted in a specific recovery of significant levels of the ligand with the vesicles. The strong decrease in radioactive ASC detected after hypotonic disruption of the vesicles or after an assay at 4 degrees C indicated that ASC was probably transported from the medium into the lumen of the membrane vesicles. The concentration kinetics of this presumptive transport process revealed a saturation curve which best fitted a biphasic model. Each phase in this model showed Michaelis-Menten type kinetics. The kinetic parameters for the different phases were calculated to be 14 and 79 mu M (K-m1 and K-m2) and 26 and 53 pmol/min . mg protein (V-max1 and V-max2). High concentrations of iso-ascorbate, dehydroascorbate (DHA) or non-labelled ASC significantly reduced the uptake of the radioactive vitamin. It was demonstrated that sugar or amino acid carriers are not involved in the ASC transport reaction. Generation of transmembrane cation gradients (H+, K+, Ca2+, Na+) or addition of sulfhydryl reagents (pCMBS or NEM) did not affect the ASC uptake in any way. It is suggested that ASC is taken up by a facilitated diffusion mechanism.
E-info
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