The electrochemical proton gradient in Mycoplasma cells

Area of Science:

• Biochemistry
• Cellular Physiology
• Microbiology

Background:

• The electrochemical proton gradient (delta mu H+) is vital for cellular energy transduction.
• Mycoplasma species, known for their minimal genomes, offer a unique model for studying fundamental cellular processes.

Purpose of the Study:

• To determine the electrochemical proton gradient (delta mu H+) in glycolyzing Mycoplasma mycoides var. Capri cells.
• To investigate the contributions of the transmembrane pH gradient (delta pH) and membrane potential (delta psi) to delta mu H+.
• To confirm the role of chemiosmotic phenomena in energy transduction in Mycoplasma.

Main Methods:

• Measurement of delta pH using transmembrane distribution of weak acids (acetate, butyrate) and a weak base (methylamine) via flow dialysis and filtration.
• Determination of delta psi using distribution of lipophilic cation Ph3MeP+ and Rb+/K+ with valinomycin.
• Inhibition of delta pH using DCCD, CCCP, and nigericin.

Main Results:

• Glycolyzing Mycoplasma cells maintain an alkaline internal pH (0.5 units higher) and a negative membrane potential (-85 mV).
• The resulting electrochemical proton gradient (delta mu H+) is approximately -115 mV.
• Despite external pH changes altering delta psi and delta pH, delta mu H+ remained relatively constant due to compensatory mechanisms.

Conclusions:

• Mycoplasma mycoides var. Capri cells effectively utilize an electrochemical proton gradient for energy transduction.
• Chemiosmotic phenomena are confirmed to play a significant role in energy transduction across Mycoplasma membranes.
• The stability of delta mu H+ suggests robust homeostatic mechanisms within Mycoplasma cells.