The Respiratory Chain of Plant Mitochondria

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Abstract
Redox changes of the flavoproteins of mung bean (Phaseolus aureus) mitochondria were measured by differential absorbance at 468 to 493 nanometers and by fluorescence emission above 500 nanometers excited at 436 nanometers. Four flavoproteins are distinguishable by the ratio of their fluorescence to absorbance changes, and by their requirement, or lack of it, for energy-linked reverse electron transport for reduction by succinate. Two flavoproteins are reduced by succinate in fully depleted mitochondria which lack the capacity for reverse electron transport. These are designated Fpha and Fphf and have fluorescence to absorbance ratios of 0 and 1.4, respectively. The two flavoproteins have the same half-time for oxidation, but Fphf is reduced more slowly than Fpha by substrate in the presence of cyanide. One flavoprotein with a fluorescence to absorbance ratio of 0 is not reduced by succinate in anaerobic, fully depleted mitochondria, but is rapidly reduced on subsequent addition of malate; it is designated Fpm. The fourth distinguishable flavoprotein component is reducible by succinate in an energy-linked reaction, even in partially depleted mitochondria. This component has a fluorescence to absorbance ratio of 3.8 and is designated Fp1f. In addition to these four flavoproteins reducible by substrates, there is a highly fluorescent flavin-containing component in or associated with these mitochondria, which is rapidly reduced by dithionite.