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1.
The cyanmet hybrid hemoglobins alpha(2)beta(+CN)(2) and alpha(+CN)(2)beta(2) are widely held to be similar or equivalent in structure and subunit interactions to the partially oxygen-liganded species alpha(2)(beta * O(2))(2) and (alpha * O(2))(2)beta(2), respectively. An analysis of precise data on oxygen binding to the cyanmet hybrids and normal hemoglobin shows that if this is the case, then cooperative ligand binding in hemoglobin is more properly described by some model of the sequential type than by any twostate concerted model.  相似文献   

2.
Hemoglobin A(2) (alpha(2)delta(2)) in New World primates represents about 1/160 to 1/16 of total hemoglobin and, by virtue of this low proportion, is presumed to be functionally unimportant. Nonetheless, A(2) exhibits genetic polymorphism by electrophoresis in three out of five genera, whereas the major component, hemoglobin A (alpha(2)beta(2)), is electrophoretically invariant. Moreover, in four genera, including man, the evolutionary accumulation of mutations has been greater in delta than in beta Such findings suggest that both polymorphism and evolutionary changes can accrue to an effectively functionless and thus selectively nearly netutral gene.  相似文献   

3.
Stuidy of the amino acid composition and amino-terminal residue in the abnormal peptide of an electrophoretically slow hemoglobin revealed that the globin's structure was alpha(2)beta(2)(121 Lys) (Obeta). This hemoglobin had been provisionally classified as Hb E or as a new heemoglobin. The clinical significance of this abnormality is not yet defined.  相似文献   

4.
Structural characterization of a new variant of human hemoglobin (adult), designated hemoglobin Freiburg, indicates the deletion of the valyl residue No. 23 from an otherwise normal beta-chain. The formula may be written (alpha2)beta(2)(23val-0). The abnormal hemoglobin is present with hemoglobin A in the proposita and in two of her three living children, but is not detectable in her parents. We postulate that this variant represents a triplet base deletion which most likely resulted from an unequal crossing-over between two normal betachain loci during meiosis in one of the parents of the proposita.  相似文献   

5.
A cell-free protein-synthesizing system made from rabbit reticulocytes was used to incorporate (14)C-amino acids into hemoglobin. Electrophoretic analyses of the soluble products of this cell-free system revealed a fraction containing rabbit (14)C-alpha chains in addition to the rabbit (14)C-hemoglobin. The addition of isolated human hemoglobin beta chains to this system during active synthesis inhibited the release of newly synthesized rabbit (14)C-beta chains into solution from the ribosome fraction. This inhibition was possibly a result of hybrid hemoglobin formation between rabbit alpha and human beta chains. A model of hemoglobin construction in which soluble alpha chains are intermediates is suggested. These alpha chains may aid in the release of beta chains from the polyribosomes during the completion of the hemoglobin molecule.  相似文献   

6.
Activation of hemoglobin C synthesis in sheep marrow culture   总被引：6，自引：0，他引：6  
Erythropoietin preferentially stimulates hemoglobin C synthesis in suspension cultures of marrow cells from sheep homozygous for hemoglobin A; the amount of synthesis is dependent on the dose of erythropoietin and is blocked by antiserum to erythropoietin. The results provide the first in vitro evidence that erythropoietin mediates the hemoglobin A --> C "switch" in sheep and indicate that bone marrow cultures may be used to investigate the mechanisms involved in the preferential gene activation characteristic of the hemoglobin A --> C system.  相似文献   

7.
Class IA phosphoinositide 3-kinases (PI3Ks) are a family of p85/p110 heterodimeric lipid kinases that generate second messenger signals downstream of tyrosine kinases, thereby controlling cell metabolism, growth, proliferation, differentiation, motility, and survival. Mammals express three class IA catalytic subunits: p110alpha, p110beta, and p110delta. It is unclear to what extent these p110 isoforms have overlapping or distinct biological roles. Mice expressing a catalytically inactive form of p110delta (p110delta(D910A)) were generated by gene targeting. Antigen receptor signaling in B and T cells was impaired and immune responses in vivo were attenuated in p110delta mutant mice. They also developed inflammatory bowel disease. These results reveal a selective role for p110delta in immunity.  相似文献   

8.
The mechanisms that control localization of marginal zone (MZ) B cells are poorly understood. Here we show that MZ B cells express elevated levels of the integrins LFA-1 (alphaLbeta2) and alpha4beta1 and that they bind to the ligands ICAM-1 and VCAM-1. These ligands are expressed within the MZ in a lymphotoxin-dependent manner. Combined inhibition of LFA-1 and alpha4beta1 causes a rapid and selective release of B cells from the MZ. Furthermore, lipopolysaccharide-triggered MZ B cell relocalization involves down-regulation of integrin-mediated adhesion. These studies identify key requirements for MZ B cell localization and establish a role for integrins in peripheral lymphoid tissue compartmentalization.  相似文献   

9.
Electron diffraction patterns of the fullerene C(60) in the gaseous state have been obtained by volatilizing it from a newly designed oven-nozzle at 730 degrees C. The many peaks of the experimental radial distribution curve calculated from the scattered intensity are completely consistent with icosahedral symmetry for the free molecule. On the basis of this symmetry assumption, least-squares refinement of a model incorporating all possible interatomic distances led to the values r(g)(C(1)-C(2)) = 1.458(6) angstroms (A) for the thermal average bond length within the five-member ring (that is, for the bond fusing five- and six-member rings) and r(g)(C(1)-C(6)) = 1.401(10) A for that connecting five-member rings (the bond fusing six-member rings). The weighted average of the two bond lengths and the difference between them are the values 1.439(2) A and 0.057(6) A, respectively. The diameter of the icosahedral sphere is 7.113(10) A. The uncertainties in parentheses are estimated 2sigma values.  相似文献   

10.
Normal human articular cartilage synthesizes only one type of a chain, which exhibits the chromatographic behavior of the alpha(l)(II) chains described for chick and bovine cartilage. Osteoarthritic cartilage, on the other hand, synthesizes in addition a collagen containing alpha(2) chains and beta components. The different structural features of the two types of collagen may account for some of the functional defects of osteoarthritic cartilage.  相似文献   

11.
Interleukin-2 (IL-2) induces cytolytic activity and proliferation of human blood lymphocytes. Yet, prior to activation, these cells do not express IL-2 receptors recognized by monoclonal antibodies to the Tac antigen. A novel glycoprotein (IL-2R beta), identified on several lymphocytoid cell lines, has the ability to bind IL-2 alone and to associate with Tac antigen (IL-2R alpha) to form high-affinity IL-2 receptors. It is now reported that IL-2R beta is expressed on both circulating T lymphocytes and large granular lymphocytes in quantities approximately proportional to their responsiveness to IL-2. Studies of the responses of these cells to IL-2 suggest that IL-2R beta mediates the initial phase of induction of lymphokine activated killer (LAK), natural killer (NK), and proliferative activities. Subsequently, IL-2R alpha is induced and functional high-affinity IL-2 receptors are expressed.  相似文献   

12.
The alpha 2 and beta 2 adrenergic receptors, both of which are activated by epinephrine, but which can be differentiated by selective drugs, have opposite effects (inhibitory and stimulatory) on the adenylyl cyclase system. The two receptors are homologous with each other, rhodopsin, and other receptors coupled to guanine nucleotide regulatory proteins and they contain seven hydrophobic domains, which may represent transmembrane spanning segments. The function of specific structural domains of these receptors was determined after construction and expression of a series of chimeric alpha 2-,beta 2-adrenergic receptor genes. The specificity for coupling to the stimulatory guanine nucleotide regulatory protein lies within a region extending from the amino terminus of the fifth hydrophobic domain to the carboxyl terminus of the sixth. Major determinants of alpha 2- and beta 2-adrenergic receptor agonist and antagonist ligand binding specificity are contained within the seventh membrane spanning domain. Chimeric receptors should prove useful for elucidating the structural basis of receptor function.  相似文献   

13.
Interleukin-2 (IL-2) binds to two distinct receptor molecules, the IL-2 receptor alpha (IL-2R alpha, p55) chain and the newly identified IL-2 receptor beta (IL-2R beta, p70-75) chain. The cDNA encoding the human IL-2R beta chain has now been isolated. The overall primary structure of the IL-2R beta chain shows no apparent homology to other known receptors. Unlike the IL-2R alpha chain, the IL-2R beta chain has a large cytoplasmic region in which a functional domain (or domains) mediating an intracellular signal transduction pathway (or pathways) may be embodied. The cDNA-encoded beta chain binds and internalizes IL-2 when expressed on T lymphoid cells but not fibroblast cells. Furthermore, the cDNA gives rise to the generation of high-affinity IL-2 receptor when co-expressed with the IL-2R alpha chain cDNA.  相似文献   

14.
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15.
The mechanism of T cell depletion during infection with the human immunodeficiency virus (HIV) is unclear. Examination of the repertoire of T cell receptor V (variable) regions in persons infected with HIV revealed the absence of a common set of V beta regions, whereas V alpha usage was normal. The lack of these V beta segments did not appear to correlate with opportunistic infections. The selective elimination of T cells that express a defined set of V beta sequences may indicate the presence of an HIV-encoded superantigen, similar to those encoded by the long terminal repeat of the mouse mammary tumor virus.  相似文献   

16.
GABAA (gamma-aminobutyric acid A)-benzodiazepine receptors expressed in mammalian cells and assembled from one of three different alpha subunit variants (alpha 1, alpha 2, or alpha 3) in combination with a beta 1 and a gamma 2 subunit display the pharmacological properties of either type I or type II receptor subtypes. These receptors contain high-affinity binding sites for benzodiazepines. However, CL 218 872, 2-oxoquazepam, and methyl beta-carboline-3-carboxylate (beta-CCM) show a temperature-modulated selectivity for alpha 1 subunit-containing receptors. There were no significant differences in the binding of clonazepam, diazepam, Ro 15-1788, or dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) to all three recombinant receptors. Receptors containing the alpha 3 subunit show greater GABA potentiation of benzodiazepine binding than receptors containing the alpha 1 or alpha 2 subunit, indicating that there are subtypes within the type II class. Thus, diversity in benzodiazepine pharmacology is generated by heterogeneity of the alpha subunit of the GABAA receptor.  相似文献   

17.
An empirical model describing the diffusion kinetics of oxygen in silicate minerals under hydrothermal conditions has been established for temperatures between 773 and 1073 Kelvin at 100 megapascals of water pressure. The equation, log D = alpha + (beta/T) + [(gamma + (delta/T))Z], where D is the diffusion coefficient, alpha, beta, gamma, and delta are constants, T is the Kelvin temperature, and Z is the total ionic porosity, may be used to predict diffusion coefficients, in most cases to within the reported experimental reproducibility of a factor of 2. For oxygen diffusion, alpha = -2, beta = -3.4 x 10(4)K, gamma = -0.13, and delta = 6.4 x 10(2)K, for D in square centimeters per second. Limited data for the diffusion of argon in silicates suggest that the model describes this system as well.  相似文献   

18.
 从真菌云芝子实体中分离鉴定了6个化合物和1个混合物,分别为：(22E,24R)-ergosta-7,22-dien-3β-ol（1）、 (22E, 24R)-ergosta-6,22-dien-3β,5α,8α-triol（2）、5α,6α-epoxy-(22E,24R)-ergosta-8,22-dien-3β,7α-diol（3）、二十四碳酸（4）、二十六碳酸（5）和α,α-trehalose（6）;混合物可推测主要由russulamide（7）、ascolipid C（8）、ascolipid D（9）组成。除化合物1外,其余化合物均为该种首次分离得到。  相似文献   

19.
Hemoglobin Ann Arbor, in which arginine replaces leucine in position 80 of the a chain, occurs in aflected individuals in low proportion to hemoglobin A. Biosynthetic studies were perforined on reticulocytes of a patient heterozygous for this hemoglobin. These studies suggested that the low percentage of hemoglobin Ann Arbor is prinlarily due to preferential destruction of the abnormal component. The reduced concentration of alpha Ann Arbor chains was also reflected in a decreased synthesis of normal beta chains.  相似文献   

20.
Injection of two 25-microgram-per-gram doses of the hemolytic agent phenylhydrazine reduced the hemoglobin level and the erythrocyte count to less than 1 percent of normal tadpole and young blullfrog blood. These anemic animals survive for weeks with little change in overall metabolism. A slow recovery of hemoglobin levels was observed. The implications of this observation for comparative biochemistry are considered.  相似文献   

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