Auxin Regulation of a Proton Translocating ATPase in Pea Root Plasma Membrane Vesicles

Abstract

Pea root microsomal vesicles have been fractionated on a Dextran step gradient to give three fractions, each of which carries out ATP-dependent proton accumulation as measured by fluorescence quenching of quinacrine. The fraction at the 4/6% Dextran interface is enriched in plasma membrane, as determined by UDPG sterol glycosyltransferase and vanadate-inhibited ATPase. The vanadate-sensitive phosphohydrolase is not specific for ATP, has a Km of about 0.23 millimolar for MgATP, is only slightly affected by K+ or Cl- and is insensitive to auxin. Proton transport, on the other hand, is more specific for ATP, enhanced by anions (NO3- > Cl-) and has a Km of about 0.7 millimolar. Auxins decrease the Km to about 0.35 millimolar, with no significant effect on the Vmax, while antiauxins or weak acids have no such effect. It appears that auxin has the ability to alter the efficiency of the ATP-driven proton transport.