Cd. Faraday et Rm. Spanswick, DIFFERENTIAL STIMULATION BY CL- OF H-MEMBRANE VESICLES FROM MAIZE (ZEA-MAYS L) ROOTS( TRANSPORT AND ATPASE ACTIVITY IN PURIFIED PLASMA), Journal of Experimental Botany, 46(290), 1995, pp. 1169-1176
Maize (Zea mays L.) root plasma membranes purified by the aqueous poly
mer two-phase technique have previously been shown to be very low in t
onoplast H+-ATPase and H+-PPase activities. Western blots of a similar
preparation showed that, compared to a microsomal fraction, there was
practically no reaction with antibodies to the tonoplast enzymes, but
a strong reaction with an antibody to the plasma membrane H+-ATPase.
Freeze/thaw treatment of the plasma membrane vesicles increased the pr
oportion with an inside-out orientation to about 40%. This preparation
was used to demonstrate that substitution of KCl for K2SO4 resulted i
n a 14-fold stimulation of H+ transport, but an increase in ATPase act
ivity of less than 10%. In contrast to its effect on tonoplast vesicle
s, Cl- had only a small effect on the membrane potential of plasma mem
brane vesicles, assayed by oxonol V fluorescence quench recovery. To a
ccount for the apparent variability in the H+/ATP coupling ratio, it m
ay be necessary to devise a model that takes into consideration the po
ssibility of non-linear behaviour with respect to the membrane potenti
al of the proton leak and/or of slip in the ATPase.