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Mammalian hibernation 总被引:6,自引:0,他引:6
J Nedergaard B Cannon 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1990,326(1237):669-85, discussion 685-6
In mammalian hibernation, the body temperature approaches that of the surroundings, allowing large savings in energy costs of basal metabolism and eliminating the need for heat production to compensate for heat loss. During entry into hibernation, heat production ceases while the body temperature set-point gradually decreases during slow-wave sleep. In the hibernating phase, the animal copes with problems concerning the maintenance of ion gradients, possible membrane phase transitions and the risk of ventricular fibrillation. In the arousal phase, the main part of the heat and practically all the necessary substrate comes from brown adipose tissue. The hibernation season is preceded by a preparatory phase. It may be concluded that hibernation is a practical, and perhaps even enviable, solution to a mammalian problem. 相似文献
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Chemical, spectroscopic, and structural studies have established the metallothioneins (MTs) to be a widely occurring family
of polypeptidic bioinorganic structures. They are distinguished by an extremely high metal (Zn, Cd, Cu) and Cys content and
by the arrangement of these components in metal-thiolate clusters. By structural criteria the MTs have recently been subdivided
into three classes (Fowler et al.,Experientia Suppl.
52, 19–22, 1987). Class I MTs include mammalian MTs and related forms. Class II MTs display no such relationships, and Class
III MTs are atypical polypeptides made up of repetitive γ-glutamylcysteinyl units. Amino acid sequences of over 50 MTs are
now known. In mammals, over 55% of the residues, including the 20 Cys, are conserved. Mammalian MTs are genetically polymorphous.
Thus, in human tissues and cell lines closely related structures of ten functional isoMTs have been determined either by amino
acid or nucleotide sequencing. A comparable degree of polymorphism also exists in the rabbit. Mammalian MTs have been inferred
to bind a total of seven bivalent metal ions (Me) through thiolate coordination in two separate clusters, i.e., Me(II)3(Cys)9 and Me(II)4(Cys)11. This two-cluster model has now fully been confirmed by the spatial structures of rat MT-2 and rabbit MT-2a determined by
2D NMR spectroscopy in aqueous solution. 相似文献
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ELI C. MINKOFF 《Zoological Journal of the Linnean Society》1976,58(2):147-158
The superordinal level can be used to great advantage in the taxonomy of mammals and other groups. Of the two cohorts of placental mammals, the Unguiculata is divided into six superorders: Archonta (Gregory's Archonta plus Lipotyphla), Glires, Ferae (including Delta-theridia and Carnivora), Paratheria (Edentata and Pholidota), Ganodonta, and an unnamed group for the Lagomorpha plus Anagalida. The cohort Ungulata is divided much as in Simpson (1945), with an additional superorder (Mutica) for the whales and with a superorder Amblypoda, separate from the Paenungulata, and corresponding to Romer's (1966) order of that name. 相似文献
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Muhammad Khalid Salamat Carola Munoz-Montesino Mohammed Moudjou Human Rezaei Hubert Laude Vincent Béringue Michel Dron 《朊病毒》2013,7(2):131-135
Upon prion infection, abnormal prion protein (PrPSc) self-perpetuate by conformational conversion of α-helix-rich PrPC into β sheet enriched form, leading to formation and deposition of PrPSc aggregates in affected brains. However the process remains poorly understood at the molecular level and the regions of PrP critical for conversion are still debated. Minimal amino acid substitutions can impair prion replication at many places in PrP. Conversely, we recently showed that bona fide prions could be generated after introduction of eight and up to 16 additional amino acids in the H2-H3 inter-helix loop of PrP. Prion replication also accommodated the insertions of an octapeptide at different places in the last turns of H2. This reverse genetic approach reveals an unexpected tolerance of prions to substantial sequence changes in the protease-resistant part which is associated with infectivity. It also demonstrates that conversion does not require the presence of a specific sequence in the middle of the H2-H3 area. We discuss the implications of our findings according to different structural models proposed for PrPSc and questioned the postulated existence of an N- or C-terminal prion domain in the protease-resistant region. 相似文献
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Mammalian beta-galactosidases 总被引:4,自引:0,他引:4
F Chytil 《Biochemical and biophysical research communications》1965,19(5):630-636
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Mammalian metalloendopeptidases 总被引:1,自引:0,他引:1
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Sulfoconjugates occur ubiquitously as sulfopolysaccharides, sulfolipids and sulfoproteins. A variety of sulfotransferases
catalyze the sulfation process with 3’-phosphoadenosine 5’-phosphosulfate as the sulfate donor. Sulfatases that catalyze the
desulfation of different sulfoconjugates are known to be deficient in a number of genetic storage disorders. 相似文献
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The X and Y chromosomes of the musk shrew are the two largest in the complement and they regularly form a single chiasma during meiosis. This chiasma is located in the short arms of the X and Y, both of which show partial C-banding at meiosis. The in vitro incorporation of 5-bromodeoxyuridine/tritiated thymidine during late S reveals that the non-C-band region of the Y finishes replication later than the C-band positive heterochromatin. During meiosis, the sex bivalent opens out early in pachytene to reveal a single chiasma which persists until late metaphase-I. In surface-spread, silver-stained meiocytes, the sex bivalent morphology changes from a phase of extensive pairing to one which includes a visible chiasma through a brief diffuse stage. Observations on C-banded meiocytes show a shift in the sex pair from a C-band positive to a negative state as compared to their corresponding somatic pattern. Comparable changes are also observed in the sex bivalents of other mammals which undergo a chiasmatic exchange. This suggests that in addition to pairing homology, an alteration in the chromatin configuration may be necessary for crossing over to occur between the sex chromosomes. 相似文献
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Three mammalian hyaluronan (HA) synthase genes, HAS1, HAS2, and HAS3, have been cloned and expressed, allowing the mechanisms for regulation of HA biosynthesis and function to be studied. The hyaluronan synthase (HAS) isoforms differ in kinetic characteristics and product size. The expression of each HAS isoform is controlled in a different fashion when mammalian cells are stimulated by various cytokines and the expression patterns are both spatially and temporally regulated during embryonic development. The existence of three different HAS isoforms with different characteristics implies that the broad range of biological and physiological roles performed by HA are regulated by controlling the activities and expression of the HAS isoforms. This review focuses on recent findings on the regulatory mechanisms for controlling HA biosynthesis and provides new insights into the enzymic basis for the functional regulation of HA. 相似文献
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Mammalian cyclin-dependent kinases 总被引:15,自引:0,他引:15
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Alan E. Tomkinson David S. Levin 《BioEssays : news and reviews in molecular, cellular and developmental biology》1997,19(10):893-901
DNA joining enzymes play an essential role in the maintenance of genomic integrity and stability. Three mammalian genes encoding DNA ligases, LIG1, LIG3 and LIG4, have been identified. Since DNA ligase II appears to be derived from DNA ligase III by a proteolytic mechanism, the three LIG genes can account for the four biochemically distinct DNA ligase activities, DNA ligases I, II, III and IV, that have been purified from mammalian cell extracts. It is probable that the specific cellular roles of these enzymes are determined by the proteins with which they interact. The specific involvement of DNA ligase I in DNA replication is mediated by the non-catalytic amino-terminal domain of this enzyme. Furthermore, DNA ligase I participates in DNA base excision repair as a component of a multiprotein complex. Two forms of DNA ligase III are produced by an alternative splicing mechanism. The ubiqitously expressed DNA ligase III-α forms a complex with the DNA single-strand break repair protein XRCC1. In contrast, DNA ligase III-β, which does not interact with XRCC1, is only expressed in male meiotic germ cells, suggesting a role for this isoform in meiotic recombination. At present, there is very little information about the cellular functions of DNA ligase IV. 相似文献
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