dicumarol and antimycin

Hyoscyamus albus hairy roots secrete riboflavin under Fe-deficient conditions. To determine whether this secretion was linked to an enhancement of respiration, both riboflavin secretion and the reduction of 2,3,5-triphenyltetrazolium chloride (TTC), as a measure of respiration activity, were determined in hairy roots cultured under Fe-deficient and Fe-replete conditions, with or without aeration. Appreciable TTC-reducing activity was detected at the root tips, at the bases of lateral roots and in internal tissues, notably the vascular system. TTC-reducing activity increased under Fe deficiency and this increase occurred in concert with riboflavin secretion and was more apparent under aeration. Riboflavin secretion was not apparent under Fe-replete conditions. In order to examine which elements of the mitochondrial electron transport chain might be involved, the effects of the respiratory inhibitors, barbiturate, dicoumarol, malonic acid, antimycin, KCN and salicylhydroxamic acid (SHAM) were investigated. Under Fe-deficient conditions, malonic acid affected neither root growth, TTC-reducing activity nor riboflavin secretion, whereas barbiturate and SHAM inhibited only root growth and TTC-reducing activity, respectively, and the other compounds variously inhibited growth and TTC-reducing activity. Riboflavin secretion was decreased, in concert with TTC-reducing activity, by dicoumarol, antimycin and KCN, but not by SHAM. In Fe-replete roots, all inhibitors which reduced riboflavin secretion in Fe-deficient roots showed somewhat different effects: notably, antimycin and KCN did not significantly inhibit TTC-reducing activity and the inhibition by dicoumarol was much weaker in Fe-replete roots. Combined treatment with KCN and SHAM also revealed that Fe-deficient and Fe-replete roots reduced TTC in different ways. A decrease in the Fe content of mitochondria in Fe-deficient roots was confirmed. Overall, the results suggest that, under conditions of Fe deficiency in H. albus hairy roots, the alternative NAD(P)H dehydrogenases, complex III and complex IV, but not the alternative oxidase, are actively involved both in respiration and in riboflavin secretion.

Topics: Antimycin A; Barbiturates; Cyanates; Dicumarol; Electron Transport; Hyoscyamus; Iron Deficiencies; Malonates; Plant Roots; Riboflavin; Salicylamides

This is the confirmation of an earlier indication (Mersel, M., Malviya, A.N., Hindelang, C. and Mandel, P. (1984) Biochim. Biophys. Acta 778, 144-154) that the plasma membrane of astrocytes in primary cultures is endowed with DT-diaphorase (EC 1.6.99.2) activity. It is observed that the NADPH-2,6-dichloroindophenol diaphorase activity found in the isolated plasma membrane is not inhibited by dicoumarol. DT-diaphorase-type activity is also observed on the cell surface employing dichloroindophenol as external electron acceptor and it is found to be a dicoumarol-sensitive NADH dehydrogenase.

Topics: Animals; Antimycin A; Astrocytes; Cell Membrane; Cells, Cultured; Dicumarol; NAD(P)H Dehydrogenase (Quinone); NADH, NADPH Oxidoreductases; Quinone Reductases; Rats; Rotenone

Menadione and vicasol completely restore the respiration rate of rat liver mitochondria after its inhibition by rotenone. Under the same conditions these compounds stimulate oxygen consumption by rabbit heart mitochondria up to 40% of the maximal uncoupled respiration rate in the presence of 5 mM glutamate and up to 30% of the maximal uncoupled respiration rate in a lymphocyte suspension containing glucose. Cyanide and dicumarol, specific inhibitors of DT-diaforase, completely suppress the stimulating effect of menadione and vicasol in isolated mitochondria and by 50% in lymphocyte suspensions. The DiS-C3-(5) fluorescence in lymphocyte suspensions suggests that the menadione and vicasol-induced respiration is capable of supporting the mitochondrial transmembrane potential in lymphocytes. Thus, in different tissues menadione and vicasol can restore oxygen consumption in mitochondria, in which the first and second energy coupling sites are inhibited.

Topics: Animals; Antimycin A; Dicumarol; Female; Fluorescent Dyes; In Vitro Techniques; Lymphocytes; Mitochondria, Heart; Mitochondria, Liver; Oxidative Phosphorylation; Oxygen Consumption; Rats; Rotenone; Uncoupling Agents; Vitamin K; Vitamin K 3