Evidence for an electrogenic ATPase in microsomal vesicles from pea internodes

Area of Science:

• Plant Physiology
• Membrane Transport
• Biochemistry

Background:

• Microsomal vesicles from plant tissues are essential for studying membrane transport mechanisms.
• Understanding the bioenergetics of plant cells requires elucidating the function of membrane-bound ATPases.

Purpose of the Study:

• To investigate the effect of adenosine triphosphate (ATP) on the transmembrane electropotential of pea internode microsomal vesicles.
• To characterize the mechanism of ATP-stimulated ion transport in these vesicles.

Main Methods:

• Monitoring transmembrane electropotential using the equilibrium distribution of the permeant anion thiocyanate (SCN-).
• Assessing the specificity of ATP effects against other nucleoside phosphates.
• Evaluating the impact of ATPase inhibitors and protonophores on SCN- uptake.
• Determining the optimal pH for ATP-mediated SCN- uptake.

Main Results:

• ATP strongly hyperpolarized the vesicle membrane potential, indicated by increased SCN- uptake.
• This stimulation was specific to ATP and sensitive to ATPase inhibitors and protonophores.
• Oligomycin showed minimal effect, while toluene/ethanol treatment permeabilized vesicles.
• Optimal ATP effect on SCN- uptake occurred around pH 7.0.

Conclusions:

• Pea internode microsomal vesicles possess a membrane-bound ATPase.
• This ATPase couples ATP hydrolysis to electrogenic ion transport, likely of protons (H+).
• The findings contribute to understanding energy transduction in plant membranes.