Plant Physiology 80:727-731 (1986)
© 1986 American Society of Plant Biologists
Articles
Kinetics of Ca2+/H+ Antiport in Isolated Tonoplast Vesicles from Storage Tissue of Beta vulgaris L. 1
Eduardo Blumwald and
Ronald J. Poole
Plant Molecular Biology Center, McGill University, Montreal, Quebec, Canada H3A 1B1,
Department of Biology, McGill University, Montreal, Quebec, Canada H3A 1B1
Artificial pH gradients across tonoplast vesicles isolated from storage tissue of red beet (Beta vulgaris L.) were used to study the kinetics of a Ca2+/H+ antiport across this membrane. Ca2+-dependent H+ fluxes were measured by the pH-dependent fluorescence quenching of acridine orange.  pH-dependent Ca2+ influx was measured radiometrically. Both H+ efflux and Ca2+ influx displayed saturation kinetics and an identical dependence on external calcium with apparent Km values of 43.9 and 41.7 micromolar, respectively. Calcium influx was unaffected by an excess of Mg2+ but was inhibited by La3+ > Mn2+ > Cd2+. The apparent Km for external calcium was greatly affected (5-fold) by internal pH in the range of 6.0 to 6.5 and a transmembrane effect of internal proton binding on the affinity for external calcium is suggested.
1 Supported by the Natural Sciences and Engineering Research Council of Canada and the Department of Education of Quebec.
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