Abstract
Abstract Molecular oxygen uptake was initiated by adding NADPH (1 mM) to the buffered medium containing 0.6 μ M spinach ferredoxin:NADP + oxidoreductase and 20 μ M quinone (plastoquinone-2, decyl-plastoquinone, decyl-ubiquinone, or duroquinone). At pH 7.7 the rate of oxygen uptake was 2- to 12-fold higher during an initial phase (V 1 ) than in a subsequent phase (V 2 ). Except for duroquinone, the initial rate of oxygen consumption was ca. 2.7-fold higher in alkaline than in acidic medium. Ferredoxin was not essential, although it stimulated the reaction investigated. Oxygen uptake was not detectable with plastoquinone-9 or α-tocoquinone. The possible mechanisms of the NADPH and ferredoxin:NADP oxidoreductase dependent reduction of some quinones and their reoxidation are discussed.
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