Identification and characterisation of two allelic forms of human alcohol dehydrogenase 2

The human alcohol dehydrogenase system is comprised of multiple forms that catalyse the oxidation/reduction of a large variety of alcohols and aldehydes. A transition that results in an Ile308Val substitution was identified in the human ADH2 gene by single-strand conformation polymorphism analysis. Screening a Swedish population revealed that Val308 was the most frequent allele (73%), and site-directed mutagenesis was used to obtain both allelozymes, which were expressed in Escherichia coli for characterisation. Thermostability was assayed by activity measurements and circular dichroism spectroscopy. The results showed that the 308Val substitution decreases protein stability, as compared to the Ile308 variant, an effect also demonstrated during prolonged storage. Ethanol, octanol, 12-hydroxydodecanoic acid and all-trans retinol were used as model substrates and, generally, slightly higher Km values were observed with Val at position 308. Finally, homology modelling, from mouse ADH2, further supported the decreased stability of the Val308 variant and located position 308 in the subunit interface of the molecule and in the vicinity of the active-site pocket entrance. In conclusion, the Ile308Val substitution represents a novel functional polymorphism within the human alcohol dehydrogenase gene cluster that may affect the metabolism of ethanol and other substrates.     

Myelin sheaths: glycoproteins involved in their formation,maintenance and degeneration

Myelin sheaths are formed around axons by extending, biochemically modifying and spiraling plasma membranes of Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS). Because glycoproteins are prominent components of plasma membranes, it is not surprising that they have important roles in the formation, maintenance and degeneration of myelin sheaths. The emphasis in this review is on four integral membrane glycoproteins. Two of them, protein zero (P0) and peripheral myelin protein-22 (PMP-22), are components of compact PNS myelin. The other two are preferentially localized in membranes of sheaths that are distinct from compact myelin. One is the myelin-associated glycoprotein, which is localized at the inside of sheaths where it functions in glia-axon interactions in both the PNS and CNS. The other is the myelin-oligodendrocyte glycoprotein, which is preferentially localized on the outside of CNS myelin sheaths and appears to be an important target antigen in autoimmune demyelinating diseases such as multiple sclerosis. Received 8 April 2002; received after revision 13 May 2002; accepted 22 May 2002     

Differential display analysis of gene expression in invertebrates

Screening for differentially expressed genes is a straightforward approach to study the molecular basis for changes in gene expression. Differential display analysis has been used by investigators in diverse fields of research since it was developed. Differential display has also been the approach of choice to investigate changes in gene expression in response to various biological challenges in invertebrates. We review the application of differential display analysis of gene expression in invertebrates, and provide a specific example using this technique for novel gene discovery in the nematode Caenorhabditis elegans.     

Glioma cell activation by Alzheimer's peptide Abeta1-42, alpha1-antichymotrypsin,and their mixture

We compared the effects ofAlzheimer's peptide (Abeta1-42), a,-antichymotrypsin (ACT) and an ACT/Abeta1-42 mixture on human glioma DK-MG cells. The solution of Abeta (5 microM) formed by 2-h incubation at room temperature induced tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6 levels by 55 and 45%, respectively, and increased gelatinase B activity by 67%, while exposure of cells to the ACT/Abeta1-42 mixture (1:10 molar ratio ACT: Abeta1-42) under the same experimental conditions showed no effect on IL-6 levels or gelatinase B activity, but strongly induced TNF-alpha (by 190%), compared to the controls. Stimulation of the cells with Abeta1-42 alone, but not with ACT, increased by about 20% low-density lipoprotein (LDL) uptake and mRNA levels for LDL receptor and HMG-CoA reductase, while the ACT/Abeta1-42 mixture significantly increased LDL uptake (by 50%), up-regulated mRNA levels for LDL receptor and HMG-CoA reductase by 48 and 63%, respectively, and increased lipid accumulation by about 20-fold. These data suggest a possible new role for Abeta in Alzheimer's disease through its interaction with the inflammatory reactant, ACT.     

Microbial cycling of volatile organic sulfur compounds

Microbial cycling of volatile organic sulfur compounds (VOSCs), especially dimethyl sulfide (DMS) and methanethiol (MT), is intensively studied because these compounds play an important role in the processes of global warming, acid precipitation, and the global sulfur cycle. VOSC concentrations in freshwater sediments are low due to the balance between the formation and degradation of these compounds. These reactions occur for the greater part at the oxic/anoxic interphase of sediment and water column. In contrast to marine ecosystems, where dimethylsulfoniopropionate is the main precursor of MT and DMS, in freshwater ecosystems, VOSCs are formed mainly by methylation of sulfide and to a lesser extent from the degradation of S-containing amino acids. One of the major routes for DMS and MT formation through sulfide methylation is anaerobic O-demethylation of methoxylated aromatic compounds. Inhibition studies have revealed that the major part of the endogenously produced MT and DMS is degraded anaerobically by methanogens. The major bacterial groups involved in formation and consumption of VOSCs are described.     

HIV-1 superinfection despite broad CD8+ T-cell responses containing replication of the primary virus

Early treatment of acute HIV-1 infection followed by treatment interruptions has shown promise for enhancing immune control of infection. A subsequent loss of control, however, allows the correlates of protective immunity to be assessed. Here we show that sudden breakthrough of plasma viraemia occurred after prolonged immune containment in an individual infected with HIV-1 at a time when 25 distinct CD8+ T-cell epitopes in the viral proteins Gag, RT, Integrase, Env, Nef, Vpr, Vif and Rev were being targeted. Sequencing of the virus in plasma and cells showed that superinfection with a second clade-B virus was coincident with the loss of immune control. This sudden increase in viraemia was associated with a decline in half of the CD8+ T-cell responses. The declining CD8+ T-cell responses were coupled with sequence changes relative to the initial virus that resulted in impaired recognition. Our data show that HIV-1 superinfection can occur in the setting of a strong and broadly directed virus-specific CD8+ T-cell response. The lack of cross-protective immunity for closely related HIV-1 strains, despite persistent recognition of multiple CD8 epitopes, has important implications for public health and vaccine development.     

Multiple ionization of atom clusters by intense soft X-rays from a free-electron laser

Intense radiation from lasers has opened up many new areas of research in physics and chemistry, and has revolutionized optical technology. So far, most work in the field of nonlinear processes has been restricted to infrared, visible and ultraviolet light, although progress in the development of X-ray lasers has been made recently. With the advent of a free-electron laser in the soft-X-ray regime below 100 nm wavelength, a new light source is now available for experiments with intense, short-wavelength radiation that could be used to obtain deeper insights into the structure of matter. Other free-electron sources with even shorter wavelengths are planned for the future. Here we present initial results from a study of the interaction of soft X-ray radiation, generated by a free-electron laser, with Xe atoms and clusters. We find that, whereas Xe atoms become only singly ionized by the absorption of single photons, absorption in clusters is strongly enhanced. On average, each atom in large clusters absorbs up to 400 eV, corresponding to 30 photons. We suggest that the clusters are heated up and electrons are emitted after acquiring sufficient energy. The clusters finally disintegrate completely by Coulomb explosion.     

旅游民族志

通过旅游民族志研究对当代旅游人类学所面临的一些问题进行探讨,亦即不仅在旅游人类学范围内考察有关民族志问题,而且将这些问题置于人类学的当代实践之中,包括:长期和短期的民族志研究、民族志田野作业的传统、民族志的时空策略、旅游民族志中的特殊问题等。