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61.
The ability of salts to inhibit the O2-evolution activity of PS II preparations is shown to parallel closely the Hofmeister series, suggesting that inhibition is related to the solubility of the 16, 24 and 33 kDa proteins in these salt solutions. An examination of the effect of salt inactivation on the low temperature multiline EPR signal indicates that the release of either the 16 and 24 kDa proteins, or additionally the 33 kDa protein blocks or greatly reduces the efficiency of the advancement of the water-splitting complex to the S2-state; under some conditions, this inhibition is reversible. 相似文献
62.
In Photosystem II preparations at low temperature we were able to generate and trap an intermediate state between the S1 and S2 states of the Kok scheme for photosynthetic oxygen evolution. Illumination of dark-adapted, oxygen-evolving Photosystem II preparations at 140 K produces a 320-G-wide EPR signal centered near g = 4.1 when observed at 10 K. This signal is superimposed on a 5-fold larger and somewhat narrower background signal; hence, it is best observed in difference spectra. Warming of illuminated samples to 190 K in the dark results in the disappearance of the light-induced g = 4.1 feature and the appearance of the multiline EPR signal associated with the S2 state. Low-temperature illumination of samples prepared in the S2 state does not produce the g = 4.1 signal. Inhibition of oxygen evolution by incubation of PS II preparations in 0.8 M NaCl buffer or by the addition of 400 μM NH2OH prevents the formation of the g = 4.1 signal. Samples in which oxygen evolution is inhibited by replacement of Cl? with F? exhibit the g = 4.1 signal when illuminated at 140 K, but subsequent warming to 190 K neither depletes the amplitude of this signal nor produces the multiline signal. The broad signal at g = 4.1 is typical for a spin system in a rhombic environment, suggesting the involvement of non-heme Fe in photosynthetic oxygen evolution. 相似文献
63.
In the presence of Cl?, the severity of ammonia-induced inhibition of photosynthetic oxygen evolution is attenuated in spinach thylakoid membranes (Sandusky, P.O. and Yocum, C.F. (1983) FEBS Lett. 162, 339–343). A further examination of this phenomenon using steady-state kinetic analysis suggests that there are two sites of ammonia attack, only one of which is protected by the presence of Cl?. In the case of Tris-induced inhibition of oxygen evolution only the Cl? protected site is evident. In both cases the mechanism of Cl? protection involves the binding of Cl? in competition with the inhibitory amine. Anions (Br? and NO?3) known to reactive oxygen evolution in Cl?-depleted membranes also protect against Tris-induced inhibition, and reactivation of Cl?-depleted membranes by Cl? is competitively inhibited by ammonia. Inactivation of the oxygen-evolving complex by NH2OH is impeded by Cl?, whereas Cl? does not affect the inhibition induced by so-called ADRY reagents. We propose that Cl? functions in the oxygen-evolving complex as a ligand bridging manganese atoms to mediate electron transfer. This model accounts both for the well known Cl? requirement of oxygen evolution, and for the inhibitory effects of amines on this reaction. 相似文献
64.
The results of our present study indicate that 1 alpha, 25-dihydroxyvitamin D3[1 alpha, 25(OH)2D3] directly induces fusion of mouse alveolar macrophages without any participation of T-lymphocytes by a mechanism involving RNA and protein synthesis but not DNA synthesis. We have reported that 1 alpha, 25(OH)2D3 induces fusion of alveolar macrophages by a direct mechanism and by a spleen cell-mediated indirect mechanism [(1983) Proc. Natl. Acad. Sci. USA 80, 5583-5587]. Alveolar macrophages pretreated with or without anti-Thy 1.2 antibody and complement fused similarly when they were incubated with 1 alpha, 25(OH)2D3. The vitamin suppressed DNA synthesis, but it significantly enhanced RNA and protein synthesis. The 1 alpha, 25(OH)2D3-induced fusion was blocked by adding actinomycin D or cycloheximide, but not by hydroxyurea. 相似文献
65.
The H+/O ratio of proton translocation linked to the oxidation of succinate by mitochondria 总被引:1,自引:0,他引:1
Raymond Wootton 《FEBS letters》1984,178(2):187-192
In a recent communication Lehninger and co-workers (Costa, L.E., Reynaferje, B., and Lehninger, A.L. (1984) J. Biol. Chem. 259, 4802-4811) reported values approaching 8 for the H+/O ratio of vectorial proton ejection from rat liver mitochondria respiring with succinate. Here we present a rigorous analysis of these measurements which reveals that they may significantly overestimate the true H+/O stoicheiometry. 相似文献
66.
The rotational freedom of tryptophan residues in protein-ligand complexes was studied by measuring steady-state fluorescence anisotropies under conditions of oxygen quenching. There was a decrease in the oxygen bimolecular quenching constant upon complexation of trypsin and alpha-chymotrypsin with proteinaceous trypsin inhibitors, of lysozyme with N-acetylglucosamine (NAG) and di(N-acetyl-D-glucosamine) ((NAG)2) and of hexokinase with glucose. Binding of the bisubstrate analogue N-phosphonacetyl-L-aspartate (PALA) to aspartate transcarbamylase (ATCase) and binding of biotin to avidin resulted in increased oxygen quenching constants. The tryptophan of human serum albumin (HSA) in the F state was more accessible to oxygen quenching than that in the N state. With the exception of ATCase, the presence of subnanosecond motions of the tryptophan residues in all the proteins is suggested by the short apparent correlation times for fluorescence depolarization and by the low apparent anisotropies obtained by extrapolation to a lifetime of zero. Complex formation evidently resulted in more rigid structures in the case of trypsin, alpha-chymotrypsin and lysozyme. The effects of glucose binding on hexokinase were not significant. Binding of biotin to avidin resulted in a shorter correlation time for the tryptophan residues. The N --> F transition in HSA resulted in a more rigid environment for the tryptophan residue. Overall, these changes in the dynamics of the protein matrix and motional freedom of tryptophan residues due to complex formation and subsequent conformational changes are in the same direction as those observed by other techniques, especially hydrogen exchange. Significantly, the effects of complex formation on protein dynamics are variable. Among the limited number of cases we examined, the effects of complex formation were to increase, decrease or leave unchanged the apparent dynamics of the protein matrix. 相似文献
67.
Summary Germination of microsclerotia ofMacrophomina phaseolina was observed at O2 concentrations of 16% or higher in autoclaved soil. Germination was delayed but otherwise unaffected as O2 decreased from 21 to 16% and was in all cases complete in 32 hours. Laboratory-produced microsclerotia consistently germinated more rapidly and seemed more independent of O2 concentrations within the range that permitted germination than naturallyproduced microsclerotia.Population changes in soil as measured by microsclerotial counts were inversely correlated with depth of interment and reduced O2 concentration. Our inability to detect significantly growth responses ofM. phaseolina in non autoclaved soil was apparently related to limited O2 although other possibilities are discussed.Contribution of the Missouri Agricultural Experiment Station Scientific Journal Series No. 9124. 相似文献
68.
Aerobic denitrification: a controversy revived 总被引:37,自引:0,他引:37
During studies on the denitrifying mixotroph, Thiosphaera pantotropha, it has been found that this organism is capable of simultaneously utilizing nitrate and oxygen as terminal electron acceptors in respiration. This phenomenon, termed aerobic denitrification, has been found in cultures maintained at dissolved oxygen concentrations up to 90% of air saturation.The evidence for aerobic denitrification was obtained from a number of independant experiments. Denitrifying enzymes were present even in organisms growing aerobically without nitrate. Aerobic yields on acetate were higher (8.1 g protein/mol) without than with (6.0 g protein/mol) nitrate, while the anaerobic yield with nitrate was even lower (4 g protein/mol). The maximum specific growth rate of Tsa. pantotropha was higher (0.34 h-1) in the presence of both oxygen (>80% air saturation) and nitrate than in similar cultures not supplied with nitrate (0.27 h-1), indicating that the rate of electron transport to oxygen was limiting. This was confirmed by oxygen uptake experiments which showed that although the rate of respiration on acetate was not affected by nitrate, the total oxygen uptake was reduced in its presence. The original oxygen uptake could be restored by the addition of denitrification inhibitors.Dedicated to Professor Dr. H.-G. Schlegel on the occasion of his 60th birthday 相似文献
69.
Synopsis Oxygen uptake (VO2) during graded hypoxia, rate of hypoxia acclimation, breathing frequency (fR), breath volume (VS, R) and gill ventilation (VG) were measured in Hoplias malabaricus. Normoxia and hypoxia acclimated fish had similar and constant VO2 and VG in a range of water PO2 from 150 to 25 mmHg. Hypoxia acclimated fish showed significantly higher VO2 in severe hypoxia (PO2 <15 mmHg). Normoxia acclimated fish showed symptoms similar to hypoxic coma after 1 h of exposure to water PO2 of 10 mmHg whereas the same symptoms were observed only at PO2 of 5 mmHg for fish acclimated to hypoxia. Fish required 14 days to achieve full acclimation to hypoxia (PO2 ≥25 mmHg). Lowering of water PO2 from 150 to 25 mmHg resulted in normoxic fish showing a 3–2 fold increase in VG. The increase was the result of an elevation in VS, R rather than fR. Among normoxia acclimated specimens, small fish showed a higher VG per unit weight than the large ones in both normoxia (PO2 =150 mmHg) and hypoxia (PO2 = 15 mmHg). A decrease in the ventilatory requirement (VG/VO2) with increased body weight was recorded in hypoxia (PO2 = 15 mmHg). 相似文献
70.
A mechanism for indirect allosteric action of charged effectors on substrate binding to a macromolecule is proposed. It is
accounted for by electrostatic interaction among effectors in the solution, away from their receptors. The possibility of
the mechanism proposed is tested in the allosteric action of univalent salt and 2,3-diphosphoglycerate on oxygen binding to
hemoglobin. A model for electrostatic interaction between these two effectors in the solution and for their overall effect
on oxygen binding is introduced. The 2,3-diphosphoglycerate binding constant to deoxygenated hemoglobin as a function of univalent
salt concentration and the median ligand activity as a function of the concentration of univalent salt and 2,3-diphoshoglycerate
are calculated and compared with experimental data. The obtained results indicate that electrostatic interaction in the solution
may significantly contribute to indirect allosteric action of charged effectors.
Partly presented at the “11th FEBS Meeting” in Copenhagen, August 1977 相似文献