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Results for “Redox potential”

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At least 451 records · Page 25Linked to original sources
PubMed1978

Flash-induced changes in the in vivo bacteriochlorophyll fluorescence yield at low temperatures and low redox potentials in carotenoid-containing strains of photosynthetic bacteria.

The changes in the in vivo bacteriochlorophyll fluorescence induced by a Xenon flash at low temperatures (77--200 K) with the "primary" acceptor X chemically prereduced have been examined in whole cells of several species of photosynthetic bacteria which contain carotenoids absorbing in the visible part of the absorption spectrum. Two groups of species with different behaviour could be distinguished. In both cases a flash-induced rise of the fluorescence yield was observed with X prereduced at 77 k; as the temperature was increased the ratio of the maximum fluorescence (FM) and the basal fluorescence (F0) decreased and the kinetics of the decay of the high fluorescent state, as observed during the tail of the flash, apparently accelerated. Of the species examined the flash-induced changes in fluorescence-yield kinetics appeared to occur at higher temperatures in the members of one group (Chromatium vinosum, Rhodopseudomonas gelatinosa and Rhodopseudomonas palustris) than in the members of the other (Rhodopseudomonas palustris) than in the members of the other (Rhodopseudomonas sphaeroides and Rhodospirillum rubrum). These effects are interpreted in terms of the light-induced generation of triplet states within the reaction centre. It is suggested that the species-dependent differences may reflect differences in the molecular organisation of the reaction centre. It was found that in all species the reaction centre carotenoid triplet does not act as a fluorescence quencher under these conditions.

Bacteriochlorophylls↗
PubMed1980

The redox potentials of the b-type cytochromes of higher plant chloroplasts.

1. In fresh chloroplasts,three b-type cytochromes exist. These are b-559HP (lambda max, 559 nm; Em at pH 7, +370 mV; pH-independent Em), b-559LP (lambda max, 559 nm; Em at pH 7, +20 mV; pH-independent Em) and b-563 (lambda max, 563 nm; Em at pH 7, -110 mV; pH-independent Em), b-559HP may be converted to a lower potential form (lambda max, 559 nm; Em at pH 7, +110 mV; pH-independent Em). 2. In catalytically active b-f particle preparations, three cytochromes exist. These are cytochrome f (lambda max, 554 nm; Em at pH 7, +375 mV, pK on oxidised cytochrome at pH 9), b-563 (lambda max, 563 nm; Em at pH 7, -90 mV, small pH-dependence of Em) and a b-559 species (lambda max, 559 nm, Em at pH 7, +85 mV; pH-independent Em). 3. A positive method of demonstration and estimation of b-559LP in fresh chloroplasts is described which involves the use of menadiol as a selective reductant of b-559LP.

Chloroplasts↗
PubMed1986

Determination of the redox potential and diffusion coefficient of the protein plastocyanin using optically transparent filar electrodes.

Direct and mediated electrolysis of the protein plastocyanin at a gold filar electrode is described. The filar electrode used is of a unique design that allows potentiometric measurements, steady-state voltammetry and absorption spectrophotometry to be performed on a few microliters of solution containing 0.1-1.0 mM protein. As a result, we have determined the formal potential and diffusion coefficient of the blue copper protein, plastocyanin, to be 372 +/- 5 mV vs. normal hydrogen electrode and 8.9 X 10(-7) cm2 X s-1, respectively. The same value of the formal potential is obtained from a steady-state current experiment, an equilibrium spectrophotometric experiment, and a twin-electrode steady-state spectrophotometric experiment. The fact that the diffusion coefficient is measured under conditions of steady-state current, results in significant improvement in signal to background over techniques that monitor a transient current, while the potential is changing.

Electrochemistry↗