The electrochemical potential across mycoplasmal membranes

Area of Science:

• Microbiology
• Biochemistry
• Cellular Physiology

Background:

• The electrochemical proton gradient is crucial for cellular energy production.
• Mycoplasmas possess unique membrane structures and metabolic pathways.

Purpose of the Study:

• To investigate and quantify the electrochemical proton gradient (delta p) across mycoplasmal membranes.
• To determine the contributions of transmembrane electric potential (delta psi) and transmembrane proton gradient (delta pH) to delta p.
• To elucidate the mechanism of delta p generation in mycoplasmas.

Main Methods:

• Utilized potential-sensitive cyanine dyes to measure membrane potentials (delta psi).
• Employed [14C]5,5-dimethyl oxazolidine-2,4-dione distribution to determine intracellular pH and delta pH.
• Calculated the proton-motive potential (delta p) using the formula: delta p = delta psi - (A x delta pH).

Main Results:

• Measured delta psi values of -48 mV (Mycoplasma mycoides subspecies capri, Mycoplasma gallisepticum) and -28 mV (Acholeplasma laidlawii).
• Determined delta pH values indicating intracellular alkalinity relative to the extracellular medium (e.g., 0.4 at external pH 7.0).
• Calculated delta p values of -72 mV for M. mycoides subspecies capri/M. gallisepticum and -52 mV for A. laidlawii.

Conclusions:

• The proton-motive potential (delta p) in mycoplasmas is primarily generated by a membrane-bound, proton-translocating ATPase.
• This ATPase functions via hydrolysis of ATP produced during glycolysis, driving proton extrusion.
• The findings provide insights into the bioenergetics and membrane transport mechanisms of mycoplasmas.