Oxidative phosphorylation by membrane vesicles from Bacillus alcalophilus.

Area of Science:

• Biochemistry
• Microbiology
• Bioenergetics

Background:

• Bacillus alcalophilus utilizes t-malate as a carbon source.
• Membrane vesicles from this bacterium can be loaded with ADP and Pi.
• Proton motive force (delta-mu-H+) is a key driver for ATP synthesis in many organisms.

Purpose of the Study:

• To investigate ATP synthesis in Bacillus alcalophilus.
• To determine the conditions under which ATP synthesis occurs.
• To elucidate the mechanism of ATP synthesis, particularly its dependence on proton motive force.

Main Methods:

• Preparation of ADP and Pi-loaded membrane vesicles from t-malate-grown Bacillus alcalophilus.
• Energization of vesicles using ascorbate/N,N,N',N'-tetra-methyl-P-phenylenediamine.
• Measurement of ATP synthesis across a range of external pH values.
• Calculation of phosphate potentials (delta Gp) and protonmotive force (delta-mu-H+).
• Inhibition studies using KCN, gramicidin, and N,N1-dicyclohexylcarbodiimide.
• Direct pH monitoring and fluorescence methods to track proton translocation.

Main Results:

• ATP synthesis was observed in a broad pH range (6.0-11.0).
• Significant ATP synthesis occurred at low protonmotive force (delta-mu-H+) as low as -30 mV.
• Phosphate potentials reached 11-12 kcal/mol at pH 10.5 and 9.0.
• ATP synthesis was inhibited by specific chemical agents (KCN, gramicidin, DCCD).
• Inward proton translocation was directly correlated with ATP synthesis.
• No requirement for Na+ or K+ was detected.

Conclusions:

• Bacillus alcalophilus possesses a proton-translocating ATPase.
• This ATPase is capable of functioning efficiently under conditions of low proton motive force.
• The findings highlight a unique mechanism for energy conversion in B. alcalophilus, independent of sodium or potassium ions.