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排序方式: 共有114条查询结果,搜索用时 31 毫秒
91.
Isabel Llorente-Garcia Tchern Lenn Heiko Erhardt Oliver L. Harriman Lu-Ning Liu Alex Robson Sheng-Wen Chiu Sarah Matthews Nicky J. Willis Christopher D. Bray Sang-Hyuk Lee Jae Yen Shin Carlos Bustamante Jan Liphardt Thorsten Friedrich Conrad W. Mullineaux Mark C. Leake 《BBA》2014
Chemiosmotic energy coupling through oxidative phosphorylation (OXPHOS) is crucial to life, requiring coordinated enzymes whose membrane organization and dynamics are poorly understood. We quantitatively explore localization, stoichiometry, and dynamics of key OXPHOS complexes, functionally fluorescent protein-tagged, in Escherichia coli using low-angle fluorescence and superresolution microscopy, applying single-molecule analysis and novel nanoscale co-localization measurements. Mobile 100–200 nm membrane domains containing tens to hundreds of complexes are indicated. Central to our results is that domains of different functional OXPHOS complexes do not co-localize, but ubiquinone diffusion in the membrane is rapid and long-range, consistent with a mobile carrier shuttling electrons between islands of different complexes. Our results categorically demonstrate that electron transport and proton circuitry in this model bacterium are spatially delocalized over the cell membrane, in stark contrast to mitochondrial bioenergetic supercomplexes. Different organisms use radically different strategies for OXPHOS membrane organization, likely depending on the stability of their environment. 相似文献
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Metabolic stereoisomeric inversion of ibuprofen in mammals 总被引:1,自引:0,他引:1
Studies on the mechanism and enzymology of metabolic ibuprofen isomerization constituted the focus of this investigation. Comparative in vivo studies revealed that this biotransformation proceeded via a proton abstraction mechanism in all tested species of mammals, which is in agreement with the previous reports. Direct evidence supporting this conclusion stemmed from the in vitro epimerization of ibuprofen-CoA thioester in rat liver homogenates. Chemically synthesized (R)-ibuprofen-CoA thioester was rapidly transformed to its (S)-counterpart by subcellular hepatic preparations. Examination of this epimerase activity in various rat tissue homogenates indicated that this enzyme was highly tissue specific. This biochemical reaction mainly took place in the liver and kidney, whereas low levels of enzyme activity were associated with other tissues. Nevertheless, the liver and kidney homogenates failed to invert (R)-ibuprofen directly even in the presence of all the necessary cofactors. Presumably, the failure to characterize this bioconversion was due to the lack of enzymatic acyl-CoA synthesis in these homogenates. It is noteworthy that the '2-arylpropionyl-CoA epimerase' catalyzed the transformation from either direction and with high turnover rates. The catalytic efficiency of (S)-ibuprofen CoA epimerization appeared to be greater than that of the (R)-counterpart. These in vitro findings suggest that the step of acyl-CoA formation assume a pivotal role in controlling the stereoselectivity and efficiency of the in vivo metabolism. As the responsible acyl-CoA synthetase(s) in different species of animals may exert the reaction with different degrees of enantiomeric preference and efficiency, the resulting stereochemical outcome and metabolic rates of this bioinversion vary accordingly. Consequently, in guinea pigs, this biotransformation proceeds in both directions with nearly equal efficiency, whereas it is virtually unidirectional and slow in humans. Currently, the purification and characterization of this novel '2-arylpropionyl-CoA epimerase' from rat livers constitute the focus of this investigation. 相似文献
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Harderian letdown in male mongolian gerbils (Meriones unguiculatus) contributes to proceptive behavior 总被引:1,自引:0,他引:1
Adult female gerbils in estrus, like other female rodents, tend to engage in proceptive displays toward conspecific males. The displays, which may be interspersed with the more usual female agonistic activity, if the males are strangers, are preceded by female olfactory investigation of those head areas in the male gerbil where Harderian letdown accumulates most densely. This study explored the possibility that the male Harderian glands are a source of olfactory signals which promote proceptive behavior but suppress female agonistic behavior. Female gerbils in estrus were found to display significantly less than normal rates of proceptive behavior toward Harderianectomized males. The proceptive activity which was observed appeared to be slowed, but the typical pattern was retained. Female aggression, however, was not affected by their estrous condition or by the Harderian state of the males. Possibly Harderian letdown in male gerbils may inform females as to the reproductive competence of the males. 相似文献