Quantitative Relationship Between 9-Aminoacridine Fluorescence Quenching and Internal pH in Broken Chloroplasts

Abstract

Illuminated thylakoids create a transmembrane proton gradient by translocating protons from the outside phase into the inside one. Measurement of this inside proton concentration [H⁺]_in is not a simple problem because the thylakoids with their tiny sizes are not accessible even to the smallest proton sonde. A versatile method to evaluate pH. based on the distribution of amines was introduced by Rottenberg et. al. (Eur.J.Biochem. 25/1972/54,64,71) assuming that only the uncharged species of amines is freely permeable across the membrane. The distribution of amines upon membrane energization could be determined by:

• 1. radioactive labeling,

• 2. fluorescence quenching,

• 3. proton uptake.