Measurements of Membrane Potentials in Plant Mitochondria with the Safranine Method

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Abstract
The positively charged dye, sefranine, was used as an indicator of membrane potentials in mung bean (Phaseolus aureus) and Voodoo lily (Sauromatum guttatum) mitochondria under a variety of metabolic conditions. The spectral response of safranine was calibrated with respect to a K+ diffusion potential and was linearly related to the developed potential within the range of 50-160 mv. Respiration and ATP hydrolysis gave rise to a membrane potential of .apprx. 135 mV. Respiratory inhibitors such as cyanide and antimycin depolarized the potential, whereas rotenone had little effect. No potentials were developed during NADH-supported cyanide insensitive respiration. Apparently, safranine may be a useful spectrophotometric probe of the mitochondrial membrane potential.