Cytochrome Components & Electron Transfer in Sweet Potato Mitochondria

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Abstract
Studies on respiration and oxidatlve phosphorylation of sweet potato (Ipomoea batatas, Poir) mitochondria were extended using preparations from a white variety (Pelican Processor). Low carotenoid content of the preparations allowed relatively good spectrophotometric resolution of cytochrome components. Succinate produced a sequential reduction of mitochondrial cytochromes of the types b, c, a, and a3, as determined by difference spectra. Better resolution of cytochromes was achieved at low temperature (-196 C). Components absorbing at 549, 553, 558, 562, and 598 m[mu] were demonstrated. Oxidation of the 553, 558, and 562 mu components was inhibited by antimycin A and 2-n-heptyl-4-hydroxyqulnoline-N-oxide, thus demonstrating the difference in behavior of the 553 mu component compared to cytochrome C1. These results point further to the ubiquitous distribution of these cytochromes in tissues of higher plants; similar ones have been noted in mitochondria from a number of plant tissues. More severe effects of respiratory-chain inhibitors on oxidatlve phosphorylation, than on electron transfer by these mitochondria were noted, thus confirming observations of others. In addition, resistance of succinoxidase activity increased with time and this increase was apparently not due to an lnactivatlon of antimycln A by the particles. The latter results were Considered to support theories of alternate, non-phosphorylative shunts or pathways of electron transfer which have been proposed for plant mitochondria which exhibit inhibitor-resistant respiration.