Modification of Proton Transport Kinetics of the Plasma Membrane H +-ATPase after Adaptation of Tobacco Cells to NaCI

Abstract

Summary Plasma membrane enriched vesicle fractions were isolated on discontinuous sucrose gradients from unadapted and 428 mM NaCl adapted tobacco cells ( Nicotiana tabacum L. var. Wisconsin 38). The fractions collected from the 36/45 % interfaces were determined to be plasma membrane enriched based on analyses of marker enzyme activities. Kinetic properties of H + -transport (determined by [ 14 C]-SCN - uptake) of the plasma membrane H + -ATPase of adapted cells were substantially different than those of unadapted cells. H + transport activity of the plasma membrane H + -ATPase from NaCl adapted cells was more susceptible to substrate inhibition by free ATP (k i = 3.1 mM) than the activity of the plasma membrane H + -ATPase from unadapted cells (k i = 10 mM). The plasma membrane H + -ATPase from NaCl adapted cells exhibited an apparent K m for MgATP of 0.6 ± 0.2 mM compared with 1.76 ± 0.5 mM for the plasma membrane H + -ATPase from unadapted cells. These data indicate that the plasma membrane H + -ATPase of adapted cells can function efficiently in saline environments where increased competition for the ATP pool is presumed.