The Respiratory Chain of Plant Mitochondria

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Abstract
The oxidation-reduction potentials of the flavoproteins of skunk cabbage (Symplocarpus foetidus) mitochondria have been measured under anaerobic conditions by means of a combined spectrophotometric or fluorimetric-potentiometric method. Five components were resolved whose oxidation-reduction reactions corresponded to two-electron changes, as expected for flavoproteins. The midpoint potentials at pH 7.2 are as follows, listed in order of increasingly negative potential: +170 millivolts, +110 millivolts, +20 millivolts, −70 millivolts, and −155 millivolts. The most negative component was highly fluorescent; the other components could only be identified by their characteristic absorbance changes. In addition to these components, which are mitochondrial, variable amounts of a very highly fluorescent flavoprotein with a midpoint potential of −215 millivolts was found. This component appears to be extra-mitochondrial. The same midpoint potential values at pH 7.2 were obtained with mitochondria in the uncoupled state as in mitochondria energized with ATP in the absence of phosphate.