The Respiratory Chain Components of Higher Plant Mitochondria

Abstract

Tightly coupled mitochondria have been prepared from a variety of plant sources white potato (Solanum tuberosum), Jerusalem artichoke (Helianthus tuberosus), a cauliflower buds (Brassica oleracea), and mung bean hypocotyls (Phaseolus aureus). Mitochondria with no appreciable coupling were also prepared from skunk cabbage spadices (Symplocarpus foetidus). Room temperature difference spectra show that these mitochondria are very similar in the qualitative and quantitative composition of their electron carriers. The different cytochromes are present in the amounts of 0.1 to 0.3 m[mu]mole/mg of mitochondrial protein. The molar ratios of the different electron carriers are, on the average: 0.7:0.7:1.0:3 to 4:10 to 15 respectively for cytochrome aa3, cytochromes b, cytochromes c, flavoproteins, and pyridine nucleotides. From low temperature difference spectra carried out under particular experimental conditions, it can be deduced that these mitochondria contain 3 b cytochromes whose a bands are located at 552, 557, and 561 m[mu], and 2 c cytochromes, one of which, a c1-like cytochrome, is firmly bound to the mitochondria membrane. Cytochrome oxidase can be optically resolved into its 2 components a and a3. For all kinds of mitochondria, the rates of oxidation of succinate are similar as well as the turnover of cytochrome oxidase (50-70 sec-1), regardless of the metabolic activities of the tissues. The number of mitochondria per cell appears to be the controlling factor of the intensity of tissue respiration.