Electron Transport Mechanisms in Tobacco Roots. I. Studies on the Cytochrome and Related Systems.

Since the work of Keilin (16), several investigators have made extensive studies on the distribution and properties of cytochrome enzymes in various higher plant materials (1, 19, 20, 30). Some attempts have been made to purify cytochromes from higher plants. Goddard (7) has purified cytochrome c from wheat germ and Hill and Scarisbrick (12) have purified cytochromes b3 and c from bean leaves. Miller et al (22) have dispersed cytochrome oxidase from soybeans using sodium cholate, but no appreciable purification was accomplished. Simon (23) observed that treatment of plant mitochondria with digitonin greatly increased the cytochrome c oxidative capacity and he suggests that dispersion by digitonin increases the accessibility of cytochrome oxidase to exogenous reduced cytochrome c. No purification of cytochrome oxidase from the digitonin extracts was reported. Hackett (8) has studied electron transport enzymes in particles isolated from potatoes and has identified cytochrome oxidase, DPNH (reduced diphosphopyridine nucleotide) oxidase, diaphorase, DPNH cytochrome c reductase and succinic cytochrome c reductase. He suggests with the particulate system that electrons are transferred successively from DPNH to a flavoprotein, to an antimycin A sensitive factor, to the cytochrome system and then to oxygen. In a study of the properties of a soluble preparation from potato tissue Hackett (9) has demonstrated that extracts prepared in presence of cysteine will catalyze the oxidation of either DPNH or TPNH (reduced triphosphopyridine nucleotide) by molectular oxygen. Dialysis of the extracts caused a loss of activity. Humphreys and Conn (15) have studied the properties of a system in lupine mitochondria which catalyzed the oxidation of reduced pyridine nucleotide by molecular oxygen. There is relatively little evidence to indicate the significance of the cytochromes in the tobacco plant. Cytochrome oxidase has been identified in extracts of the tobacco plant by Webster (30) and by Miller