N. Horemans et al., CARRIER-MEDIATED UPTAKE OF DEHYDROASCORBATE INTO HIGHER-PLANT PLASMA-MEMBRANE VESICLES SHOWS TRANS-STIMULATION, FEBS letters, 421(1), 1998, pp. 41-44
The activity of the ascorbate (Asc) carrier of purified Phaseolus plas
ma membranes is demonstrated to be highly stimulated when membrane ves
icles are preloaded with Asc. Asc transport is inhibited by DTT but is
not affected by glutathione or ferricyanide, indicating that dehydroa
scorbate (DHA) is the preferred species for uptake, Asc transport in t
he loaded vesicles showed saturable kinetics with an apparent affinity
constant of 24 mu M and maximal uptake rate of 94 pmol/mg/min. Additi
on of DHA stimulated the efflux of Asc molecules from the loaded vesic
les. Together these results suggest the presence of an Asci DHA exchan
ge mechanism in higher plant: plasma membranes. (C) 1998 Federation of
European Biochemical Societies.