Quantum efficiency of light-driven proton extrusion in Halobacterium halobium. pH dependence

Area of Science:

• Biophysics
• Photochemistry
• Microbiology

Background:

• Halobacterium halobium utilizes light-driven proton pumps for energy generation.
• ATPase inhibitors are used to isolate proton extrusion mechanisms.
• Understanding quantum yield is crucial for bioenergetic studies.

Purpose of the Study:

• To determine the quantum yield for light-induced proton extrusion in Halobacterium halobium.
• To compare the efficacy of two spectrophotometric techniques for measuring proton extrusion.
• To assess the influence of pH on proton extrusion efficiency.

Main Methods:

• Spectrophotometric measurement of cell suspension transmittance using "end-on" photomultipliers.
• Spectrophotometric measurement of cell suspension reflectance using a light-integrating sphere.
• Simultaneous measurement of initial proton release rates and light absorption.

Main Results:

• The two spectrophotometric techniques yielded comparable results for quantum yield.
• Quantum yield for proton extrusion was 0.64 at pH 5.9.
• Quantum yield decreased to 0.28 at alkaline pH values.

Conclusions:

• Both transmittance and reflectance spectrophotometry are viable for measuring light-induced proton extrusion.
• Proton extrusion efficiency in Halobacterium halobium is pH-dependent, decreasing significantly in alkaline conditions.