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1.
Proc Natl Acad Sci U S A ; 86(8): 2658-62, 1989 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-2649889

RESUMO

The secondary quinone-binding site (QB site) of bacterial reaction centers from Rhodobacter sphaeroides is generally regarded to be highly specific for its native ubiquinone-10 molecule. We demonstrate here that this is a misconception rooted in the kinetic methods used to assay for occupancy of a quinone in the QB site. We show that observance of occupancy of the QB site, revealed by kinetic assay, is sensitive to the free-energy difference for electron transfer between the quinone at the primary quinone-binding site (QA site) and the QB site (-delta G0e-). For many of the compounds previously tested for binding at the QB site, the -delta G0e- between QA and QB is too small to permit detection of the functional quinone in the QB site. With an increased -delta G0e- achieved by replacing the native ubiquinone-10 at the QA site with lower-potential quinones or by testing higher-potential QB candidates, it is shown that the QB site binds and functions with the unsubstituted 1,4-benzoquinone, 1,4-naphthoquinone, and 9,10-phenanthraquinone, as well as with their various substituted forms. Moreover, quinones with the ortho-carbonyl configuration appear to function in a similar manner to quinones with the para-carbonyl configuration.


Assuntos
Proteínas de Bactérias/fisiologia , Bacterioclorofilas/fisiologia , Clorofila/análogos & derivados , Fotossíntese , Quinonas/fisiologia , Rodopseudomonas/fisiologia , Transporte de Elétrons , Complexos de Proteínas Captadores de Luz , Oxirredução , Complexo de Proteínas do Centro de Reação Fotossintética , Análise Espectral , Termodinâmica
2.
FEBS Lett ; 240(1-2): 153-8, 1988 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-3056745

RESUMO

Absorption changes at 325 nm (delta A325) induced by 15 ps laser flashes (lambda = 650 nm) in PS II membrane fragments were measured with picosecond time-resolution. In samples with the reaction centers (RCs) kept in the open state (P I QA) the signals are characterized by a very fast rise (not resolvable by our equipment) followed by only small changes within our time window of 1.6 ns. In the closed state (PI QA-) of the reaction center the signal decays with an average half-life time of about 250 ps. It is shown that under our excitation conditions (E = 2 x 10(14) photons/cm2 per pulse) subtraction of the absorption changes in closed RCs (delta A closed 325) from those in open RCs (delta A open 325) leads to a difference signal which is dominated by the reduction kinetics of QA. From the rise kinetics of this signal and by comparison with data in the literature it is inferred that QA becomes reduced by direct electron transfer from Pheo- with a time constant of about 350 +/- 100 ps.


Assuntos
Clorofila/análogos & derivados , Clorofila/fisiologia , Feofitinas/fisiologia , Proteínas de Plantas/fisiologia , Plastoquinona/fisiologia , Quinonas/fisiologia , Sistema Livre de Células , Transporte de Elétrons , Técnicas In Vitro , Cinética , Complexos de Proteínas Captadores de Luz , Oxirredução , Complexo de Proteínas do Centro de Reação Fotossintética , Plantas
4.
Am Rev Respir Dis ; 133(5): 805-8, 1986 May.
Artigo em Inglês | MEDLINE | ID: mdl-3010781

RESUMO

Leukotriene B4 (LTB4) is a metabolite of arachidonic acid that has potent chemotactic activity for polymorphonuclear leukocytes (PMN). Pulmonary oxygen toxicity is considered to be a good model of an acute inflammatory lung injury, and an increase in the number of PMN is found in the lungs acutely injured by hyperoxia. In order to estimate the role of LTB4 responsible for this influx of PMN, we measured the LTB4 by radioimmunoassay in lung lavages of rats exposed to hyperoxia for 60 h. We found that the level of LTB4 in lung lavages in rats exposed to hyperoxia for 60 h increased significantly compared with that in normoxic control rats. At the same time, the marked increase in the number of PMN in lung lavages and the decrease in the activity of NADPH-cytochrome c reductase in lung microsomes were also observed. The administration of AA861, a 5-lipoxygenase inhibitor, reduced not only the increase in LTB4 but also the increase in the number of PMN in lung lavages of rats exposed to hyperoxia for 60 h. Furthermore, treatment with AA861 also protected the decrease in the activity of NADPH-cytochrome c reductase. The effects of AA861 on these parameters were observed in a dose-dependent fashion. In addition, there is a good correlation between the level of LTB4 and the number of PMN in the lavage of rats exposed to hyperoxia for 60 h with or without AA861 administration.(ABSTRACT TRUNCATED AT 250 WORDS)


Assuntos
Benzoquinonas , Leucotrieno B4/fisiologia , Pulmão/fisiopatologia , Oxigênio/fisiologia , Animais , Feminino , Inflamação/fisiopatologia , Pulmão/imunologia , Pneumopatias/fisiopatologia , Microssomos/fisiopatologia , NADPH-Ferri-Hemoproteína Redutase/fisiologia , Neutrófilos/fisiologia , Quinonas/fisiologia , Ratos , Ratos Endogâmicos
5.
Biofizika ; 26(5): 802-8, 1981.
Artigo em Russo | MEDLINE | ID: mdl-6274422

RESUMO

Photoreduction of the intermediary electron acceptor, pheophytin (Ph), in photosystem-2 (PS-2) reaction centers of spinach chloroplasts or subchloroplast particles (TSF-II and TSF-IIa) at 220 K and Eh approximately -450 mV produces a narrow ESR signal of Ph. (g = 2.0033; delta H approximately 13 G) and a "doublet" centered at g = 2.00 with a splitting of 52 G at 7 K. The doublet (but not the narrow signal) is eliminated after extraction of lyophylized TSF-II with hexane, containing 0.1-0.2% methanol, or after extraction of Fe with LiClO4 and o-phenantroline, and the signal is restored by reconstitution with plastoquinone-A (PQ) or Fe++, respectively. The Fe removal results also in the development of a photoinduced ESR signal of PQ. (g approximately 2.0044; delta H approximately 9.2 G). The conclusion is made that the primary electron acceptor, Q, is in fact a complex PQ-Fe++ and that the exchange interaction of Ph. with PQ. -Fe++ is responsible for the ESR doublet. Photoreduction of Ph in TSF-IIa is accompanied by the 3-fold decrease in the formation of carotenoid triplet state (measured by the characteristic flash-induced absorbance changes) which is suggested to be a result of charge recombination in the pair [P680+ .PH.].


Assuntos
Carotenoides/fisiologia , Clorofila/análogos & derivados , Ferro/fisiologia , Feofitinas/fisiologia , Fotossíntese , Plastoquinona/fisiologia , Quinonas/fisiologia , Sítios de Ligação , Cloroplastos/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Oxirredução
9.
Physiol Rev ; 46(4): 662-95, 1966 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-5341714
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