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61.
The transport of ATP out of mitochondria and uptake of ADP and Pi into the matrix are coupled to the uptake of one proton (Klingenberg, M., and Rottenberg, H. (1977) Eur. J. Biochem. 73, 125--130). According to the chemiosmotic hypothesis of oxidative phosphorylation this coupling of nucleotide and Pi transport to proton transport implies that the P/O ratio for the synthesis and transport of ATP to the external medium is less than the P/O ratio for the synthesis of ATP inside mitochondria. A survey of previous determinations of the P/O ratio of intact mitochondria showed little convincing evidence in support of the currently accepted values of 3 with NADH-linked substrates and 2 with succinate. We have measured P/O ratios in rat liver mitochondria by the ADP pulse method and by 32 Pi esterification, measuring oxygen uptake with an oxygen electrode, and find values close to 2 with beta-hydroxybutyrate as substrate and 1.3 with succinate as substrate in the presence of rotenone to inhibit NADH oxidation. These values were largely independent of pH, temperature, Mg2+ ion concentration, Pi concentration, ADP pulse size, or amount of mitochondria used. We suggest that these are the true values of the P/O ratio for ATP synthesis and transport by mitochondria, and that previously reported higher values resulted from errors in the determination of oxygen uptake and the use of substrates which lead to ATP synthesis by succinate thiokinase. 相似文献
62.
Jos C. García‐Borrn Berta L. Snchez‐Laorden Celia Jimnez‐Cervantes 《Pigment cell & melanoma research》2005,18(6):393-410
The melanogenic actions of the melanocortins are mediated by the melanocortin‐1 receptor (MC1R). MC1R is a member of the G‐protein‐coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or α‐melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist‐independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light. 相似文献
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Formation of Virus Assembly Intermediate Complexes in the Cytoplasm by Wild-Type and Assembly-Defective Mutant Human Immunodeficiency Virus Type 1 and Their Association with Membranes 总被引:4,自引:0,他引:4 下载免费PDF全文
We have previously identified two distinct forms of putative viral assembly intermediate complexes, a detergent-resistant complex (DRC) and a detergent-sensitive complex (DSC), in human immunodeficiency virus type 1 (HIV-1)-infected CD4(+) T cells (Y. M. Lee and X. F. Yu, Virology 243:78-93, 1998). In the present study, the intracellular localization of these two viral assembly intermediate complexes was investigated by use of a newly developed method of subcellular fractionation. In wild-type HIV-1-infected H9 cells, the DRC fractionated with the soluble cytoplasmic fraction, whereas the DSC was associated with the membrane fraction. The DRC was also detected in the cytoplasmic fraction in H9 cells expressing HIV-1 Myr- mutant Gag. However, little of the unmyristylated Gag and Gag-Pol proteins was found in the membrane fraction. Furthermore, HIV-1 Gag proteins synthesized in vitro in a rabbit reticulocyte lysate system in the absence of exogenous lipid membrane were able to assemble into a viral Gag complex similar to that of the DRC identified in infected H9 cells. The density of the viral Gag complex was not altered by treatment with the nonionic detergent Triton X-100, suggesting a lack of association of this complex with endogenous lipid. Formation of the DRC was not significantly affected by mutations in assembly domains M and L of the Gag protein but was drastically inhibited by a mutation in the assembly I domain. Purified DRC could be disrupted by high-salt treatment, suggesting electrostatic interactions are important for stabilizing the DRC. The Gag precursor proteins in the DRC were more sensitive to trypsin digestion than those in the DSC. These findings suggest that HIV-1 Gag and Gag-Pol precursors assemble into DRC in the cytoplasm, a process which requires the protein-protein interaction domain (I) in NCp7; subsequently, the DRC is transported to the plasma membrane through a process mediated by the M domain of the matrix protein. It appears that during this process, a conformational change might occur in the DRC either before or after its association with the plasma membrane, and this change is followed by the detection of virus budding structure at the plasma membrane. 相似文献
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J. Paupério J. S. Herman J. Melo‐Ferreira M. Jaarola P. C. Alves J.B. Searle 《Molecular ecology》2012,21(24):6015-6032
Species are generally described from morphological features, but there is growing recognition of sister forms that show substantial genetic differentiation without obvious morphological variation and may therefore be considered ‘cryptic species’. Here, we investigate the field vole (Microtus agrestis), a Eurasian mammal with little apparent morphological differentiation but which, on the basis of previous sex‐linked nuclear and mitochondrial DNA (mtDNA) analyses, is subdivided into a Northern and a Southern lineage, sufficiently divergent that they may represent two cryptic species. These earlier studies also provided limited evidence for two major mtDNA lineages within Iberia. In our present study, we extend these findings through a multilocus approach. We sampled 163 individuals from 46 localities, mainly in Iberia, and sequenced seven loci, maternally, paternally and biparentally inherited. Our results show that the mtDNA lineage identified in Portugal is indeed a distinct third lineage on the basis of other markers as well. In fact, multilocus coalescent‐based methods clearly support three separate evolutionary units that may represent cryptic species: Northern, Southern and Portuguese. Divergence among these units was inferred to have occurred during the last glacial period; the Portuguese lineage split occurred first (estimated at c. 70 000 bp ), and the Northern and Southern lineages separated at around the last glacial maximum (estimated at c. 18 500 bp ). Such recent formation of evolutionary units that might be considered species has repercussions in terms of understanding evolutionary processes and the diversity of small mammals in a European context. 相似文献
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P. Cruz C. H. Mejia‐Ruiz R. Perez‐Enriquez A. M. Ibarra 《Molecular ecology resources》2002,2(3):239-241
Five polymorphic microsatellite loci were characterized for Penaeus (Litopenaeus) vannamei. Loci were isolated using a partial Sau3A1 genomic library by the sequencing of randomly selected clones and by a biotinylated (CT)10 and (GT)10 probes screening procedure. The last strategy resulted in the most useful data. About 40% of the clones showed a previously reported satellite/microsatellite (PVS1), reducing the chance of finding new microsatellite regions. Whereas two of the microsatellite loci with more than 10 alleles will be useful for mating analysis in a breeding program, the others might prove useful for population genetic studies. 相似文献
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