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31.
Characterization and properties of carnitine acyltransferases 总被引:2,自引:0,他引:2
32.
The structural properties of isolated purified rat brain synaptosomal membranes, both in the presence and absence of purified active toxin of the Mojave snake Crotalus scutulatus scutulatus, were studied by spin-label electron spin resonance techniques. The spectra from eight different positional isomers of nitroxide-labelled stearic acids, a rigid steroid androstanol, and a spin-labelled phosphatidylcholine intercalated into the synaptosomal membranes, were obtained as a function of temperature from 4-40 degrees C. The flexibility gradient (from spin-label order parameters) and polarity profile (from isotropic splitting factors) across the synaptosomal membranes, was characteristic for lipid bilayers. The nitroxide spin-labelled steroid, androstanol, intercalated into the synaptosomal membrane, revealed the abrupt onset of rapid cooperative rotation about the long axis of the molecule at 12 degrees C showing that the lipid molecules are rotating rapidly around their long axes at physiological temperatures. The presence of the Mojave toxin affected the synaptosomal membrane in a complex manner, depending upon the temperature and the position of the nitroxide label on the alkyl chain of the stearic acid probe. Mojave toxin exerted little effect on the flexibility gradient of the synaptosomal membrane at 20 degrees C, a temperature at which the acyl chain labels detected a structural change in the membranes. At temperatures lower than 20 degrees C, the Mojave toxin produced a change in the flexibility gradient of the synaptosomal membrane which indicated an increased disordering in the upper region of the membrane and a concomitant increased ordering of the acyl chains in the deeper regions of the membrane. At temperatures higher than 20 degrees C, the order profile of the synaptosomal membrane was shifted by the presence of the Mojave toxin in a manner which indicated that the outer parts of the membrane were more rigid and the inner regions more fluid, than in controls. A cross-over point for the perturbation occurred at C8-9, which is about 12-14 A into the membrane. This is the approximate depth of the hydrophobic pocket shown in pancreatic phospholipase A2 [Drenth et al. (1976) Nature (Lond.) 264, 373-377], a protein likely to be homologous to the basic subunit of the toxin. At all temperatures, rotational lipid motion was inhibited by the toxin as indicated by the steroid probe. The electron spin-resonance spin-label results are interpreted in terms of the partial penetration of the basic subunit of the intact toxin into the membrane, disordering the ordered chains at low temperature and ordering the disordered chains at physiological temperatures. The purified individual toxin subunits did not perturb the membrane lipids at physiological temperatures implying that both subunits must be associated for activity of the toxin which is confirmed by toxicity studies. 相似文献
33.
34.
Claudia Sobrevila 《Plant Systematics and Evolution》1989,166(1-2):45-67
The influence of different pollen donors on seed formation was investigated in three populations ofEspeletia schultzii that differ in environmental conditions and life history characteristics. Self pollen and pollen from different donors (< 15m apart) within each population was used in a diallel design in order to test the genetic base of seed set variation. Three measures of seed formation were used: (1) achene number; (2) proportion of filled achenes (fruits) that distinguishes between achenes with seeds and empty achenes; (3) proportion of aborted seeds that distinguishes between viable and aborted seeds. Self-pollinations resulted in empty achenes. Achene number did not vary between the different pollen donors. A bimodal pattern of filled achenes was found in two populations in two consecutive years. On the other hand, a unimodal pattern was found in crosses between more distant donors (> 30m). These patterns seems to be the results of a sporophytic incompatibility system. Seed abortion was highest at the higher elevations and seems to be correlated with elevation rather than with any genetic effect. 相似文献
35.
Olaf Rieβ Claudia Kammerbauer Lutz Roewer Viktor Steimle Adriane Andreas Ekkehard Albert Tatsuo Nagai Jörg T. Epplen 《Immunogenetics》1990,32(2):110-116
We have investigated the extent of DNA variability in intronic simple (gt)n(ga)m repeat sequences and correlated this to sequence polymorphisms in the flanking exon 2 of HLA-DRB genes. The polymerase chain reaction (PCR) was used to amplify a DNA fragment containing exon 2 and the repeat region of intron 2. The PCR products were separated on sequencing gels in order to demonstrate length hypervariability of the (gt)n(ga)m repeats. In a parallel experiment, the PCR products were cloned and sequenced (each exon 2 plus adjacent simple repeats) to characterize the simple repeats in relation to the HLA-DRB sequences. In a panel of 25 DRB1, DRB4, and DRB5 alleles new sequences were not detected. Restriction fragment length polymorphism (RFLP) subtyping of serologically defined haplotypes corresponds to translated DNA sequences in 85% of the cases, the exceptions involving unusual DR/DQ combinations. Many identical DRB1 alleles can be distinguished on the basis of their adjacent simple repeats. We found group-specific organization of the repeats: the DRw52 supergroup repeats differ from those of DRB1*0101, DRB4*0101, and DRB5*0101 alleles and from those of pseudogenes. Finally, we amplified baboon DNA and found a DRB allele with extensive similarity to DRB1 sequences of the DRw52 supergroup. The simple repeat of the baboon gene, however, resembles that of human pseudogenes. In addition to further subtyping, the parallel study of polymorphic protein and hypervariable DNA alleles may allow conclusions to be drawn on the relationships between the DRB genes and perhaps also on the theory of trans-species evolution.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession number M 34258. 相似文献
36.
37.
Marcelo Hermes-Lima Ana Claudia Tessis Adalberto Vieyra 《Origins of life and evolution of the biosphere》1990,20(1):27-41
In this paper it is shown that the adsorption of 5-adenosine monophosphate (5-AMP) onto precipitated calcium phosphate exhibits a sigmoidal profile as revealed by isotherms at 45 °C. This result indicates a cooperative behavior in the adsorption of 5-AMP. The relationship between adsorption capacity and surface area of the sedimented matrix may be interpreted as an indication that there is a monolayer of the adsorbed nucleotide on the solid surface. The pH dependence of adsorption suggests that the negatively charged phosphoryl group of 5-AMP interacts with a positively charged site (possibly Ca2+) on the matrix surface. The adsorption of the nucleotide is markedly decreased at pH values above 8.0. The Dixon-like plot of the effect of pH suggests an inhibitory role of hydroxyl ions in the adsorption of 5-AMP. At pH 7.5, other anions such as pyrophosphate, tripolyphosphate and carbamyl phosphate also inhibit the adsorption of the nucleotide, probably by interacting with its adsorption site. We suggest that these phosphorylated molecules could have played a role in chemical evolution by modulating the amount of nucleotides adsorbed onto mineral surfaces. The significance of these phenomena in chemical evolution is discussed. 相似文献
38.
The adsorption of 5′-AMP onto precipitated calcium phosphate (CaPi) requires the presence of soluble calcium and this dependence
exhibits a Michaelian-like behavior. This result suggests that the formation of a complex between 5′-AMP and free Ca2+ (CaAMP) is a prelude to the adsorption of the nucleotide in the solid matrix. At concentrations one order of magnitude higher,
Mn2+ and Mg2+ can substitute for soluble Ca2+ in the adsorption of 5′-AMP onto solid CaPi. However, when added simultaneously with 5′-AMP to a heterogeneous mixture that
contains CaPi and soluble Ca2+, Mn2+ and Mg2+ inhibit the adsorption of 5′-AMP in a concentration-dependent manner. This suggests the formation of complexes that are much
less effective for 5′-AMP adsorption than the CaAMP complex. On the other hand, Mn2+ and Mg2+ cannot promote desorption of the nucleotide attached to the precipitate in the presence of soluble Ca2+ if they are added after adsorption has attained equilibrium. Although desorption of 5′-AMP can be obtained by a sequential
dilution of the soluble phase with buffer and no nucleotide in a process that obeys a Langmuir equation, the lack of effect
of Mn2+ or Mg2+ when adsorption has attained its maximal value suggests strong interactions between the CaAMP complex and the solid matrix
when adsorption equilibrium is reached. The divalent cations present in the matrix also participate with different selectivity
in the attachment of the CaAMP complex, indicating that a cation-exchange mechanism could have acted in the modulation of
adsorptive/desorptive processes involving biomonomers and phosphate surfaces in primitive aqueous environments.
Received: 11 December 1995 / Accepted: 5 April 1996 相似文献
39.
BfpB, an outer membrane lipoprotein required for the biogenesis of bundle-forming pili in enteropathogenic Escherichia coli. 总被引:5,自引:1,他引:4 下载免费PDF全文
The bundle-forming pili (BFP) of enteropathogenic Escherichia coli are believed to play a role in pathogenesis by causing the formation of bacterial microcolonies that bind epithelial surfaces of the small intestine. This in vivo process is mimicked in vitro by the autoaggregation and localized adherence phenotypes. Expression of BFP, a member of the type IV pilus family, requires the enteroadherence factor (EAF) plasmid, which contains bfpA, the gene that encodes the principal structural subunit of BFP. Immediately downstream of bfpA are 13 open reading frames transcribed in the same direction as bfpA; together with bfpA, these compose the bfp gene cluster. Disruption of bfpB, the second open reading frame downstream of bfpA, was performed by allelic exchange. The resulting mutant, B171-8deltaB, did not exhibit the autoaggregation or localized adherence phenotype or produce BFP filaments. Thus, BfpB is required for pilus biogenesis. However, BfpA was produced at wild-type levels and processed normally by B171-8deltaB, indicating that BfpB acts at a step in the BFP biogenic pathway after production and processing of the structural subunit. Biochemical and cell fractionation studies showed that BfpB is a 58-kDa lipoprotein that is located primarily in the outer membrane. Assays of bfpA and bfpB mRNAs and protein expression showed that both genes are cotranscribed as part of an environmentally responsive operon that is regulated by growth phase and ammonium. 相似文献
40.
Xp-duplications with and without sex reversal 总被引:5,自引:0,他引:5
Annette Baumstark Gotthold Barbi Mahmoud Djalali Claudia Geerkens Beate Mitulla Torsten Mattfeldt José Carlos Cabral de Almeida Fernando Regla Vargas Juan Clinton Llerena Jr Walther Vogel Walter Just 《Human genetics》1996,97(1):79-86
Duplications in Xp including the DSS (dosage sensitive sex reversal) region cause male to female sex reversal. We investigated two patients from families with Xp duplications. The first case was one of two sisters with karyotype 46,XY, der(22), t(X;22)(p11.3;p11)mat and unambiguous female genitalia. The living sister was developmentally retarded, and showed multiple dysmorphic features and an acrocallosal syndrome. The second case was a boy with a maternally inherited direct duplication of Xp21.3-pter with the breakpoint close to the DSS locus. He had multiple abnormalities and micropenis, but otherwise unambiguous male genitalia. We performed quantitative Southern blot analysis with probes from Xp22.13 to p21.2 to define the duplicated region. Clinical, cytogenetic, and molecular data from both patients were compared with those of previously reported related cases. A comparison of the extragenital symptoms revealed no differences between patients with or without sex reversal. In both cases, the symptoms were non-specific. Among 22 patients with a duplication in Xp, nine had unambiguous female genitalia and a well-documented duplication of the DSS region. Two patients with duplication of DSS showed ambiguous external genitalia. From these data, we conclude that induction of testicular tissue may start in these patients, but that the type of genitalia depends on the degree of subsequent degeneration by a gene in DSS. 相似文献