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1.
Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones 总被引:1,自引:1,他引:0
A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer. 相似文献
2.
Phytochrome A regulates red-light induction of phototropic enhancement in Arabidopsis. 总被引:20,自引:5,他引:15 下载免费PDF全文
Phytochrome A (phyA) and phytochrome B photoreceptors have distinct roles in the regulation of plant growth and development. Studies using specific photomorphogenic mutants and transgenic plants overexpressing phytochrome have supported an evolving picture in which phyA and phytochrome B are responsive to continuous far-red and red light, respectively. Photomorphogenic mutants of Arabidopsis thaliana that had been selected for their inability to respond to continuous irradiance conditions were tested for their ability to carry out red-light-induced enhancement of phototropism, which is an inductive phytochrome response. We conclude that phyA is the primary photoreceptor regulating this response and provide evidence suggesting that a common regulatory domain in the phyA polypeptide functions for both high-irradiance and inductive phytochrome responses. 相似文献
3.
Over the past few years, new experimental approaches have reinforced the awareness among investigators that the heterogeneity of HDL particles indicates significant differences in production and catabolism of HDL particles. Recent kinetic studies have suggested that small HDL, containing two apolipoprotein A-I molecules per particle, are converted in a unidirectional manner to medium HDL or large HDL, containing three or four apolipoprotein A-I molecules per particle, respectively. Conversion appears to occur in close physical proximity with cells and not while HDL particles circulate in plasma. The medium and large HDL are terminal particles in HDL metabolism with large HDL, and perhaps medium HDL, being catabolized primarily by the liver. These novel kinetic studies of HDL subfraction metabolism are compelling in-vivo data that are consistent with the proposed role of HDL in reverse cholesterol transport. 相似文献
4.
A polymerase chain reaction mediated by a single primer: cloning of genomic sequences adjacent to a serotonin receptor protein coding region. 总被引:5,自引:2,他引:3 下载免费PDF全文
Under appropriate conditions, specific double-stranded DNA product was generated after amplification of genomic DNA sequences in a polymerase chain-like reaction that contained only a single primer. This type of amplification reaction was performed with a variety of primers and substrate DNAs. In addition to nonspecific heterogeneous products, 5 of 11 primers reproducibly directed synthesis of double-stranded DNA that corresponded to the region of the template that contained the authentic primer annealing site. Three of these amplified products were cloned and their ends were sequenced. All three contained a copy of the primer at both 5' ends, and the position of one of the primers represented the authentic primer binding site. In each case, the location of the second copy of the primer indicated that it had initially hybridized to a partially homologous sequence in the template DNA. This single primer reaction makes it possible to amplify and clone a DNA region of unknown sequence that is adjacent to a known DNA sequence. One of the single primer reaction products described here included sequence to the 5' side of the coding region of a serotonin receptor gene that contained a functional promoter. 相似文献
5.
Design of purine nucleoside phosphorylase inhibitors 总被引:2,自引:0,他引:2
Purine nucleoside phosphorylase inhibitors hold promise as specific immunosuppressive, anti-T cell leukemic, and antiuricopoietic agents. The best inhibitors available that are biologically active have Ki values from 10(-6) to 10(-7) M and fall into two categories: noncleavable nucleosides preferably iodinated at the C-5' position and C-8-substituted guanine or acycloguanosines. More potent inhibition is shown by phosphorylated acyclonucleosides that function as multisubstrate analogs, but these compounds are excluded from cells. The X-ray analysis of the human erythrocytic enzyme is beginning to reveal the nature of the active site and to explain the structure-activity relationships that have been established with analog substrates and inhibitors. 相似文献
6.
Multiple functions for sterols in Saccharomyces cerevisiae 总被引:16,自引:0,他引:16
Analyses with a yeast sterol auxotroph indicated that there are at least four different levels of function for sterol which have been designated sparking, critical domain, domain and bulk. Growth of yeast sterol auxotrophs on cholestanol is precluded unless minute amounts of ergosterol are available. We have designated this phenomenon the sparking of growth, in which cholestanol satisfies an overall membrane sterol requirement and ergosterol fulfills a high specificity sparking function. The critical domain role for sterol is observed under conditions of lanosterol supplementation where low levels of ergosterol (10-times those necessary for sparking on cholestanol) are required for growth. The sterol functions designated domain and bulk are illustrated by assessing cellular free sterol levels and plasma membrane properties of a sterol auxotroph after growth on different concentrations of exogenously supplied sterol. Plasma membranes isolated from auxotrophs grown on domain or bulk levels of sterol underwent no lipid thermotropic transitions, while plasma membranes from cells grown on critical domain levels of sterol underwent a lipid thermotropic transition, when analyzed by steady-state fluorescence anisotropy. 相似文献
7.
Alteration of high density lipoprotein subfraction distribution with induction of serum amyloid A protein (SAA) in the nonhuman primate 总被引:1,自引:0,他引:1
Overnight chair restraint results in a dramatic increase in serum amyloid A protein (apoSAA) of nonhuman primate high density lipoprotein (HDL). To determine whether apoSAA induction resulted in a displacement of indigenous HDL protein or a change in the subfraction distribution of HDL, we analyzed the characteristics of HDL subfractions in eight vervet monkeys before and 24 hr after apoSAA induction. Blood was taken from each animal before and after chair restraint to induce apoSAA. HDL was isolated from the plasma by ultracentrifugation and agarose column chromatography. The isolated HDL was subfractionated by density gradient centrifugation and five resulting subfractions were analyzed for protein and lipid content. With apoSAA induction there was a significant increase in d less than 1.09 g/ml protein, phospholipid, and free and esterified cholesterol which resulted in a 44% increase in the total mass of this subfraction. Concomitantly, there was a significant decrease in d 1.10-1.11 g/ml protein, total cholesterol, and cholesteryl ester, which resulted in a 16% decrease in the total mass of the subfraction. The response of the d 1.10-1.11 and d greater than 1.12 g/ml subfraction protein, cholesterol, and phospholipid concentrations to chair restraint for individual animals was directly proportional to their plasma HDL concentrations. Although there was a change in the HDL subfraction concentrations after chair restraint, there was no change in the lipid composition of the HDL subfractions nor in the total amount of HDL protein. However, the apoSAA/A-I ratio was significantly increased with induction while the apoA-II + C's/A-I ratio remained unchanged. The apoSAA/A-I ratio progressively increased with the density of the HDL subfraction. The protein composition of the d greater than 1.12 g/ml subfraction was changed from an average of three apoA-I and two apoA-II (or C's) molecules per particle to an average of two apoA-I, one apoA-II (or C's), and three or four apoSAA molecules per particle after chair restraint. Thus, apoSAA was predominantly associated with the denser HDL subfractions even though the lighter HDL subfractions were the most responsive in terms of changes in concentration. These data suggest that chair restraint of nonhuman primates induces apoSAA which displaces apoA-I and apoA-II or C's from HDL without altering the overall lipid and protein composition of the particle. In addition, chair restraint alters the concentration of HDL subfractions in ways that may be independent of apoSAA induction. 相似文献
8.
Distorted segregation and linkage of alcohol dehydrogenase genes in Camellia japonica L. (Theacease)
Alcohol dehydrogenase isozymes in Camellia japonica are encoded by two genes, Adh-1 and Adh-2. Both loci are expressed in seeds, and their products randomly associate into intragenic and intergenic dimers. Electrophoresis of leaf extracts reveals only the products of Adh-2. Formal genetic analysis indicated that the two Adh loci are tightly linked (combined estimate of r=0.004). Most segregations fit expected Mendelian ratios, but in some families distorted segregation was observed at Adh-1, Adh-2, or both loci. The deficient progeny class varied across families, and in two apparent backcrosses three rather than two phenotypic classes were recovered. The mechanism underlying these distortions is not known, but evidence is presented that suggests that the phenomenon is genic or segmental in nature. Plausible hypotheses include linkage of the Adh structural genes with a gametophytic self-incompatibility locus, translocation heterozygosity involving the segment bearing Adh-1 and Adh-2, or a combination of these two mechanisms. 相似文献
9.
10.