Maria Erecinska and Bayard T. Storey a Johnson Research Foundation, University of Pennsylvania, Philadelphia, Pennsylvania 19104 Abstract The oxidation kinetics of the two high potential flavo-proteins, one (Fp hf ) fluorescent and the other (Fp ha ) nonfluorescent, in mitochondria from skunk cabbage ( Symplocarpus foetidus ) spadices have been measured by combined spectrophotometry and fluorimetry. In the absence of respiratory inhibitors, both flavoproteins are oxidized at nearly the same rate with half-times between 120 and 160 milliseconds at 24 C. When slight differences in rate are observed, it is Fp ha which consistently has the shorter half-time. The presence of 0.3 millimolar KCN has no perceptible effect on the oxidation rate of either component. Antimycin A (2 nanomoles per milligram of protein) increases the oxidation half-time of Fp ha about 3-fold, but it has no effect on the oxidation half-time of Fp hf . In contrast to these two inhibitors, m -chlorobenzhydroxamic acid—an inhibitor specific to the cyanide insensitive, alternate oxidase pathway in these mitochondria—increases the oxidation half-time of Fp hf 10-fold to about 2 seconds, while increasing that of Fp ha only some 20%. This result implies that the flavoprotein Fp hf mediates electron transport to the alternate oxidase from the region of the mitochondrial respiratory chain encompassing Fp ha , ubiquinone, and the cytochromes b. The oxidation rate of cytochrome b 557 is unaffected by either m -chlorobenzhydroxamic acid or cyanide but is strongly inhibited by antimycin A. This result implies that cytochrome b 557 plays no direct role in the respiratory pathway to the alternate oxidase and is different from cytochrome b 7 found in mitochondria from the spadices of Arum maculatum.
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