Abstract
Membrane vesicles from the menaquinone‐deficient Bacillus subtilis aroD oxidize NADH at a low rate. NADH oxidation can be restored by the addition of slightly water‐soluble menaquinone and ubiquinone analogues up to saturation levels. These saturation levels differ for the different quinone analogues tested from 95 (1,4‐benzo‐ quinone) to 5316 (5‐hydroxy‐1,4‐naphthoquinone, juglon) nmol NADH × min−1× mg membrane protein−1 NADH oxidation in membrane vesicles from B. subtilis aroD restored with water‐soluble quinone analogues supplies the energy for l‐glutamate uptake. Like NADH oxidation the initial rate of l‐glutamate transport increases up to saturation levels. The highest initial rates of l‐glutamate uptake are observed after restoration with quinone analogues with a relatively low standard redox potential.
Functional reconstitution with natural, water‐insoluble, quinones can be achieved effectively by mixing quinone‐containing liposomes with membrane vesicles from B. subtilis aroD and subsequent freezing of the mixture in liquid nitrogen. The rate of NADH oxidation increased with the amount of menaquinone incorporated in the vesicles up to saturation levels. NADH oxidation via these menaquinones also supplies the energy for l‐glutamate uptake. The highest uptake rates can be obtained with menaquinone‐1 and menaquinone‐2. On the basis of efficiencies (mol NADH oxidized/mol l‐glutamate transported) menaquinones and mena‐ quinone analogues can be divided in two classes.
To class 1 belong the menaquinone analogues, menaquinone‐5 and menaquinone‐8. These compounds restore NADH oxidation with low levels of energy transduction. Efficiencies are observed which are comparable with the efficiency observed in membrane vesicles from B. subtilis W23 (120‐140) which contain the natural mena‐ quinone‐7.
To class 2 belong menaquinone‐I and menaquinone‐2, which restore NADH oxidation with high levels of energy transduction. Efficiencies are observed which are in the same range as observed with phenazine methosulphate (9‐13).
A model is proposed in which class 1 compounds feed in electrons from the outside from NADH to the Q‐cycle of the respiratory chain. Class 2 compounds donate electrons to the respiratory chain after cytochrome c and before cytochrome α‐601.
Functional reconstitution with natural, water‐insoluble, quinones can be achieved effectively by mixing quinone‐containing liposomes with membrane vesicles from B. subtilis aroD and subsequent freezing of the mixture in liquid nitrogen. The rate of NADH oxidation increased with the amount of menaquinone incorporated in the vesicles up to saturation levels. NADH oxidation via these menaquinones also supplies the energy for l‐glutamate uptake. The highest uptake rates can be obtained with menaquinone‐1 and menaquinone‐2. On the basis of efficiencies (mol NADH oxidized/mol l‐glutamate transported) menaquinones and mena‐ quinone analogues can be divided in two classes.
To class 1 belong the menaquinone analogues, menaquinone‐5 and menaquinone‐8. These compounds restore NADH oxidation with low levels of energy transduction. Efficiencies are observed which are comparable with the efficiency observed in membrane vesicles from B. subtilis W23 (120‐140) which contain the natural mena‐ quinone‐7.
To class 2 belong menaquinone‐I and menaquinone‐2, which restore NADH oxidation with high levels of energy transduction. Efficiencies are observed which are in the same range as observed with phenazine methosulphate (9‐13).
A model is proposed in which class 1 compounds feed in electrons from the outside from NADH to the Q‐cycle of the respiratory chain. Class 2 compounds donate electrons to the respiratory chain after cytochrome c and before cytochrome α‐601.
| Original language | English |
|---|---|
| Pages (from-to) | 651-657 |
| Number of pages | 7 |
| Journal | European Journal of Biochemistry |
| Volume | 125 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - 1982 |