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261.
IMMUNOGLOBULIN polypeptide chains consist of two well defined regions designated the “variable region” and the “constant region”. Whereas great diversity exists in amino-acid sequences of variable regions, the constant regions of a given subclass of heavy chains (CH)* are essentially invariant in sequence1, 2. Exceptions are the allelic forms, such as the rabbit allotypes A14 and A153, 4, where a threonine-alanine interchange occurs in the constant region of γ chains (Appella, Chersi, R. G. M. and Dubiski, in preparation). The markers unique to a chains (for example, A14-A15) are closely linked to allotypic markers at the a locus (a1, a2, a3)3, 4 which seem to be present on four different Ig heavy chain classes (α, γ, ε, µ)5–7. These puzzling observations can be explained if the a locus determinants are variable region markers which reflect genetically controlled differences in some relatively constant residues within the VH region sequences7. 相似文献
262.
Mitochondrial Ribosomes in HeLa Cells 总被引:5,自引:0,他引:5
HeLa cell mitochondria contain 60S ribosomes which seem to consist of subunits of 45S and 35S particles. The 16S and 12S RNA components are coded by mitochondrial DNA. 相似文献
263.
TRANSFORMATION of allogenic lymphocytes in mixed cultures depends chiefly on an incompatibility between the lymphocyte donors at the major histocompatibility locus in man (HL-A), mouse (H-2) and rat (H-l)1. Although the mouse H-2 locus can be divided into several regions each of which controls one or more antigenic specificities2 and two or more subloci control HL-A antigens in man3, it is not known whether all parts of the major histocompatibility locus are equally important in eliciting transformation in mixed lymphocyte cultures. We now show that capacity to elicit lymphocyte transformation is different for different parts of the mouse H-2 locus. 相似文献
264.
Demonstration of an “Excitation-Contraction Recoupling” Mechanism in Mammalian Ventricular Myocardium 总被引:1,自引:0,他引:1
A PROCESS called “excitation-contraction coupling” has been generally accepted to take place only in the direction of excitation to contraction. Through this mechanism a propagated action potential initiates an active state in skeletal or cardiac muscle and the muscle contracts. We propose that, in the mammalian ventricular myocardium at least, the process is not unidirectional and an important reverse coupling between the contractile system and the excitable plasma membrane has been overlooked. Through this feedback interaction the mode of contraction (that is, isotonic or isometric) not only determines the instantaneous electrical state of the plasma membrane, but also influences the mechanical events of the subsequent beats. Thus when Kaufmann et al.1 recorded intracellular action potentials from cat papillary muscle, the time course of the repolarization was altered depending on the mode of contraction. Some kind of contraction-excitation feedback has also been suggested by Stauch2 and Lab3,4. They showed a difference in the shape of the monophasic action potential, as recorded by a suction electrode, when comparing isotonic and isovolumic contraction of the intact ventricle. But their experimental conditions did not allow satisfactory analysis of the phenomenon. 相似文献
265.
The Structure of Calf Liver Cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>5</Subscript> at 2.8 Å Resolution 总被引:5,自引:0,他引:5
CYTOCHROME b5 is a haem-containing protein in the microsomes of liver tissue. It interacts specifically with a flavo-protein, cytochrome b5 reductase, which catalyses the transfer of electrons from NADH to the haem iron of the cytochrome1. The microsomal cytochrome b5 system has been implicated in fatty acid desaturation reactions2 and a similar system in erythrocytes may catalyse the reduction of methaemoglobin3. Calf liver cytochrome b5, solubilized by pancreatic lipase, has a molecular weight of 11,000 and consists of ninety-three amino-acids in the sequence shown in Fig. 1 (refs. 4 and 5). The haem group is non-covalently bound to the protein and can be removed reversibly by acid acetone treatment6. 相似文献
266.
KOJI NAKANISHI STEVEN BLOBSTEIN MAKOTO FUNAMIZU NOBUO FURUTACHI GEORGE VAN LEAR DEZIDER GRUNBERGER KARL W. LANKS I. BERNARD WEINSTEIN 《Nature: New biology》1971,234(47):107-109
WE wish to report that reconstituted sperm whale myoglobin prepared by the method of Breslow1 (except that pH 2 was found sufficient to remove all the haem) (I) crystallizes2 in a different habit from those prepared by the method of Rossi-Fanelli et al.3 (II) using haemin of Sigma lot 77B-0220 and our own 57Fe photoporphyrin preparation and the native myoglobin (III). Although all three form type A3 monoclinic prisms, the best developed plane is [001] for II and III, it is [100] for I. There seems to be great interest in reconstituted haemoproteins4,5, so it is important that crystallization habit may be a sensitive test for subtle changes in protein structures. 相似文献
267.
Glucagon Affinity Absorbents: Selective Binding of Receptors of Liver Cell Membranes 总被引:3,自引:0,他引:3
AFFINITY chromatography has been used in the rapid isolation of enzymes, antibodies, antigens and other ligand-binding proteins1–6. Selective adsorbents with biological specificity perhaps may best be used in the resolution and isolation of complex biological structures and important regulatory macromolecules present in cells in very low amounts. For example, polypeptide and steroid hormone receptors, drug receptors, transport proteins and repressor molecules may be well suited for study by this technique because they display specific binding functions with a high degree of affinity. 相似文献
268.
Role of the Galactose Binding Protein in Chemotaxis of <Emphasis Type="Italic">Escherichia coli</Emphasis> toward Galactose 总被引:51,自引:0,他引:51
The galactose binding protein is the part of the galactose chemoreceptor which recognizes the attractants galactose, glucose and a number of structurally related chemicals. 相似文献
269.
Additional Nucleotide Sequences in Precursor 16S Ribosomal RNA from <Emphasis Type="Italic">Escherichia coli</Emphasis> 总被引:5,自引:0,他引:5
MATURE 5S, 16S and 23S ribosomal RNA species present in E. coli ribosomes are the end products of complex biosyn-thetic pathways. They are formed by reduction in length, and methylation of longer RNA chains transcribed on the ribosomal RNA cistrons of E. coli DNA. While these modifications take place the ribosome structure is formed by progressive addition of ribosomal proteins and conformational changes in the resulting ribonucleoprotein precursor particles1. 相似文献
270.
Ribosomes,G-factor and Siomycin 总被引:13,自引:0,他引:13
G-factor interacts with the 50S ribo-somal subunit at a site which is distinct from the peptidyl transferase centre and which is inactivated by siomycin. 相似文献