ISSN:
1432-0991
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract Chemiosmotic coupling mechanisms operate in the electron transfer reactions from: nitrite to O2, NO2 − to NAD+, ascorbate to O2, NADH to O2, and NADH to NO3 −. The enzyme systems catalyzing these reactions are named NO2 −:O2 oxidoreductase, ATP-dependent NO2 −:NAD+ oxidoreductase, ascorbate:O2 oxidoreductase, NADH:O2 oxidoreductase, and NADH:NO3 − oxidoreductase, respectively. All of the oxidoreduction reactions are exergonic with the exception of the ATP-dependent NO2 −:NAD+ oxidoreductase system, which involves reversed electron flow against the thermodynamic gradients. The mechanism for nitrite oxidation was found to be quite different from that of ascorbate oxidation; both systems were insensitive, however, to rotenone, amytal, antimycin A, and 2-n-heptyl 4-hydroxyquinolineN-oxide. These compounds, on the other hand, severely inhibited the electron transfer reactions catalyzed by NADH:O2 oxidoreductase, NADH:NO3 − oxidoreductase, and the ATP-dependent NO2 −:NAD+ oxidoreductase, indicating a common pathway of electron transport in these oxidoreductase systems. Cyanide inhibited all systems except the NADH:NO3 − oxidoredctase. The uncoupler carbonyl cyanide-m-chlorophenyl hydrazone strongly inhibited NO2 −:O2 oxidoreductase and ATP-dependent NO2 −:NAD+ oxidoreductase, which indicates the involvement of energy-linked reactions in both systems; the uncoupler caused a marked stimulation of the NADH:O2 oxidoreductase and NADH:NO3 − oxidoreductase without affecting the ascorbate:O2 oxidoreductase activities.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01567916
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