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101.
S.J. Perkins C.L. Villiers G.J. Arlaud J. Boyd D.R. Burton M.G. Colomb R.A. Dwek 《Journal of molecular biology》1984,179(3):547-557
Neutron scattering studies are reported on subcomponent C1q of component C1 of human complement, and on C1, the complex of C1q with subunit C1r2C1s2. For C1q, the molecular weight was determined as 460,000. The radius of gyration at infinite contrast Rc is 12.8 nm. The Rc values for the proteolytically cleaved forms of C1q, namely the heads and the stalks, are 1.5 to 2 nm and 11 nm, respectively, and thus the axis-to-arm angle of C1q is estimated at 45 °. Neutron data for subunit C1r2C1s2 are published elsewhere. The neutron data on C1 lead to an Rc value of 12.6 nm for proenzymic C1 and a molecular weight of 820,000. The wideangle scattering curve of C1q exhibits a minimum at Q = 0.28 nm?1 and a maximum at 0.39 nm?1; on the addition of C1r2C1s2, this minimum disappears. The neutron data on C1 indicate that C1q and C1r2C1s2 have complexed with a large conformational change in one or both parts. No conformational changes can be detected on the activation of C1 by this method. 相似文献
102.
杨善元 《植物生理与分子生物学学报》1989,15(1):83-87
叶绿素b由单体聚合成多聚体后吸收光谱明显红移。叶绿素b聚集体膜在光下产生150 mV的光电位,停止照光后此电位消失速度比叶绿素a聚集体膜的慢。叶绿素b聚集体吸收光能后形成相当稳定的能化态,半生命期约几分钟。当聚集体解聚时所吸收的光能又以光的形式辐射出来。叶绿素b聚集体能化态的能量可快速而有效地传给叶绿素a聚集体,以叶绿素a的延迟发光形式释放出来。 相似文献
103.
104.
Human complement subcomponent C2: purification and proteolytic cleavage in fluid phase by C1s, C1r2-C1s2 and C1 总被引:1,自引:0,他引:1
Photosynthetic membranes contain considerable regions of high surface curvature, notably at their margins, where the average radius of curvature is about 10 nm. The proportion of total membrane lipid in the outer and inner thylakoid margin monolayers is estimated at 21% and 13%, respectively. The major thylakoid lipid, monogalactosyldiacylglycerol, is roughly cone-shaped and will not form complete lamellar bilayer phases, even in combination with other thylakoid lipids. It is proposed that this galactolipid plays a role in: (a) stabilising regions of concave curvature in thylakoids; and (b) packaging hydrophobic proteins in planar bilayer regions by means of inverted micelles. This model predicts substantial asymmetries in the distribution of lipids both across and along the thylakoid bilayer plane. 相似文献
105.
C1 inhibitor-dependent dissociation of human complement component C1 bound to immune complexes. 下载免费PDF全文
The interaction of C1 inhibitor with complement component C1 bound to immune complexes was examined by using 125I-labelled C1 subcomponents. The inhibitor binds rapidly to subcomponent C1s, and more slowly to subcomponent C1r. Formation of the C1r-C1 inhibitor complex causes rapid dissociation of subcomponents C1r and C1s from the antibody-antigen-component C1 aggregate. The rate and extent of this release are proportional to C1 Inhibitor concentration and are also dependent on ionic strength. Results obtained with purified C1 Inhibitor, plasma or serum as source of C1 Inhibitor are all closely comparable. Only slight dissociation of subcomponent C1q is observed under the same range of conditions. The implications of the release phenomenon are discussed in relation to the structure of component C1 and the possibility of differential turnover of C1 subcomponents. 相似文献
106.
1. Proenzymic C1r was purified from human plasma in a two-step technique involving indirect affinity chromatography on Sepharose Ig anti-C1s. The capacity of C1r to monomerize at pH 5.0 and to redimerize at neutral pH was used for selective elution of C1r. The yield in purified C1r was 39% from plasma; no trace of contaminating serine proteases was detected from [3H]diisopropyl phosphorofluoridate labelling of C1r. 2. C14 was able to undergo a two-way autoactivation: an intramolecular catalytic process catalysed by proenzymic C1r itself and an intermolecular reaction catalysed by activated C1r formed in the process of the reaction. DFP (5mM) and C1 Inh at a C1 Inh/C1r ratio of 1:1 were effective on the solely intermolecular activation, leading to partial inhibition of the autoactivation from proenzymic C1r: C1r formed during the activation was titrated by the inhibitors. Calcium, high ionic strength or acid pH decreased C1r activation. The pH effect was characterized by a slowed-down reaction below pH 6.0 and no net influence at values as high as 10.5. The two types of activation developed similarly as a function of pH. 3. Peripheral iodination of C1r revealed differences in label distribution between proenzymic (A chain moiety 48%, B chain moiety 52%) and activated C1r (A chain 20%, B chain 80%). Two different conformational states of C1r were also suggested by 125I-labelling at different temperatures. 相似文献
107.
Phylogenetic relationships among prokaryotic and eukaryotic catalases 总被引:13,自引:1,他引:12
Seventy-four catalase protein sequences, including 29 bacterial, 8 fungal,
7 animal, and 30 plant sequences, were compiled, and 70 were used for
phylogenetic reconstruction. The core of the resulting tree revealed
unique, separate groups of plant and animal catalases, two groups of fungal
catalases, and three groups of bacterial catalases. The only overlap of
kingdoms occurred within one branch and involved fungal and bacterial
large-subunit enzymes. The other fungal branch was closely linked to the
group of animal enzymes. Group I bacterial catalases were more closely
related to the plant enzymes and contained such diverse taxa as the
Gram-positive Listeria seeligeri, Deinocococcus radiodurans, and
gamma-proteobacteria. Group III bacterial sequences were more closely
related to fungal and animal sequences and included enzymes from a broad
range of bacteria including high- and low-GC Gram positives,
proteobacteria, and a bacteroides species. Group II was composed of
large-subunit catalases from diverse sources including Gram positives
(low-GC Bacilli and high-GC Mycobacteria), proteobacteria, and species of
the filamentous fungus Aspergillus. These data can be interpreted in terms
of two gene duplication events that produced a minimum of three catalase
gene family members that subsequently evolved in response to environmental
demands. Horizontal gene transfer may have been responsible for the group
II mixture of bacterial and fungal large-subunit catalases.
相似文献
108.
109.
Sequence variation in the guillemot (Alcidae: Cepphus) mitochondrial control region and its nuclear homolog 总被引:4,自引:0,他引:4
We describe sequence variation in the mitochondrial control region and its
nuclear homolog in three species and seven subspecies of guillemots
(Cepphus spp.). Nuclear homologs of the 5' end of the control region were
found in all individuals. Nuclear sequences were approximately 50%
divergent from their mitochondrial counterparts and formed a distinct
phylogenetic clade; the mitochondrial-nuclear introgression event must have
predated the radiation of Cepphus. As in other vertebrates, the guillemot
control region has a relatively conserved central block flanked by
hypervariable 5' and 3' ends. Mean pairwise interspecific divergence values
among control regions were lower than those in other birds. All individuals
were heteroplasmic for the number of simple tandem nucleotide repeats
(A(n)C) at the 3' end of the control region. Phylogenetic analyses suggest
that black guillemots are basal to pigeon and spectacled guillemots, but
evolutionary relationships among subspecies remain unresolved, possibly due
to incomplete lineage sorting. Describing molecular variation in nuclear
homologs of mitochondrial genes is of general interest in phylogenetics
because, if undetected, the homologs may confound interpretations of
mitochondrial phylogenies.
相似文献
110.
Pig Reticulocytes. III. Glucose permeability in naturally occurring reticulocytes and red cells from newborn piglets 总被引:1,自引:1,他引:0 下载免费PDF全文
The loss of facilitated glucose transport of red cells occurring in the newborn pig was monitored in 11 density-separated cells from birth to a 4 wk of age. At birth there was a threefold increase in glucose permeability from the lightest cells to the most dense, suggesting that cells having progressively less glucose permeability are released into the circulation as gestation proceeds. Because of extraordinary stimulation of erythropoietic activity, the uppermost top fraction constituting 2-3 percent of the total cells is composed purely of reticulocytes in the growing animal. The glucose permeability of these reticulocytes which at birth has a slow but significant rate of 3.7 μmol/ml cell x min at 25 degrees C is rapidly decreased within 3-4 days to the level of reticulocytes produced in the adult in response to phenylhydrazine assault. Moreover, reticulocytes themselves discard their membrane permeability to glucose in the course of maturation to red cells. Thus, even though reticulocytes at birth are permeable to glucose, they will become red cells practically impervious to glucose within a few days. These findings suggest that the transition from a glucose- permeable fetal state to a glucose-impermeable postnatal state is brought about by two mechanisms: (a) dilution of fetal cells by glucose-impervious cells produced coincidentally with or shortly after birth; and (b) elimination of fetal cells, which have a shorter half-life, from the circulation. 相似文献