Lipid peroxidation changes the expression of specific epitopes of apolipoprotein A-I

Incubation of human serum or high density lipoprotein (HDL) at 37 degrees C in the presence of Fe2+, Fe2+/Fe3+, or Mn2+ results in the increased immunoreactivity (up to 12-, 40-, and 80-fold, respectively) of specific apoA-I epitopes identified as 3D4 and 6B8, while Mg2+, Ca2+, or Cu2+ have minimal or nonsignificant effects. The effect of Mn2+ on the 3D4 epitope requires a specific association with lipids since it can be observed with HDL but not with apoHDL, even in the presence of other lipoproteins. The increase in immunoreactivity noted with Fe2+/Fe3+ or Mn2+ can be blocked with either EDTA or antioxidants (GSH and ascorbic acid), suggesting that it takes place during a peroxidative reaction of the lipids. The peroxidation of lipids which accompanies the increase in immunoreactivity does cross-link apoA-I both with itself and with apoA-II but does not cleave the molecule. The apoA-I-containing lipoproteins which float between 1.18 and 1.22 g/ml and have a pre B-electrophoretic migration are characterized by a very low immunoreactivity with monoclonal antibody 3D4 but are 10-fold or more responsive to Mn2+ treatment than other lipoprotein subfractions, thus demonstrating heterogeneity under oxidative conditions. Proteoliposomes containing apoA-I, cholesterol, and dilinoleyl-lecithin are sensitive to Mn2+ treatment, but not those made with dioleyl- or dimyristoyl-lecithins. However, the increase in 3D4 immunoreactivity is weak and transient and is followed by the disappearance of the epitope caused by cross-linking. We conclude that lipid peroxidation can specifically cross-link apoA-I and change its conformation and antigenicity.     

End product inhibition of hepatic 25-hydroxyvitamin D production in the rat: specificity and kinetics

The role of vitamin D metabolites in the regulation of hepatic 25-hydroxyvitamin D production was investigated by examining the effects of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and 24,25-dihydroxyvitamin D on the synthesis of [25-3H]hydroxyvitamin D by rachitic rat liver homogenates. Production of [25-3H]hydroxyvitamin D was inhibited by 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, but not by 24,25-dihydroxyvitamin D. 25-Hydroxyvitamin D increased the Km of the vitamin D-25-hydroxylase enzyme(s), while 1,25-dihydroxyvitamin D decreased the Vmax with a Ki of 88.7 ng/ml. Inhibition of hepatic 25-hydroxyvitamin D production by 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D may be another control mechanism to regulate circulating vitamin D levels.     

Are general practitioners ready to prevent the spread of HIV?

General practitioners are excellently placed to assess a person''s risk of being infected with the human immunodeficiency virus (HIV) and to give advice on reducing that risk. Their attitudes to the acquired immune deficiency syndrome (AIDS) and infection with HIV are, however, unknown. A questionnaire survey of 196 general practitioners in East Berkshire Health District was used to assess general practitioners'' readiness to undertake opportunistic health education to prevent the spread of infection with HIV. Altogether 132 replied. Sixty four of them expressed little interest in health education about HIV, and one in six would not dissent from the notion that AIDS could be controlled only by criminalising homosexuality. Only 75 of them had initiated discussions about HIV with patients. Moreover, many underestimated the risks from heterosexual sex while exaggerating the risks from non-sexual contact.Advice from general practitioners if given extensively might reduce the spread of infection with HIV. How best this may be achieved needs to be considered urgently.     

Atomic Resolution Cryo-EM Structure of β-Galactosidase

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A truncated RHAMM protein for discovering novel therapeutic peptides

The receptor for hyaluronan mediated motility (RHAMM, gene name HMMR) belongs to a group of proteins that bind to hyaluronan (HA), a high-molecular weight anionic polysaccharide that has pro-angiogenic and inflammatory properties when fragmented. We propose to use a chemically synthesized, truncated version of the protein (706–767), 7?kDa RHAMM, as a target receptor in the screening of novel peptide-based therapeutic agents. Chemical synthesis by Fmoc-based solid-phase peptide synthesis, and optimization using pseudoprolines, results in RHAMM protein of higher purity and yield than synthesis by recombinant protein production. 7?kDa RHAMM was evaluated for its secondary structure, ability to bind the native ligand, HA, and its bioactivity. This 62-amino acid polypeptide replicates the HA binding properties of both native and recombinant RHAMM protein. Furthermore, tubulin-derived HA peptide analogues that bind to recombinant RHAMM and were previously reported to compete with HA for interactions with RHAMM, bind with a similar affinity and specificity to the 7?kDa RHAMM. Therefore, in terms of its key binding properties, the 7?kDa RHAMM mini-protein is a suitable replacement for the full-length recombinant protein.     

Studies on the host-finding ability of the aphid parasitoid,Trioxys complanatus (Hym.: Braconidae) in lucerne and clover

The spotted alfalfa aphid (SAA),Therioaphis trifolii (Monell)f. maculata, was first recorded in Australia in 1977. It is a major pest of lucerne and other pasture medics but not of clover (Trifolium spp.). The parasitoidTrioxys complanatus Quilis was introduced into Australia in late 1977 as part of a biological control program for SAA and made a substantial contribution to the management of the pest. Since 1989, aphids which are individually indistinguishable from SAA have been causing substantial yield loss to clover pastures in western and south-eastern Australia. This aphid, now known in Australia as the spotted clover aphid (SCA), is genetically distinct from SAA and has a much wider host range. Populations of SCA in clover are rarely parasitised byT. complanatus. A series of experiments was undertaken to determine whether the greater susceptibility of SAA in lucerne than of SCA in clover to parasitisation byT. complanatus is due to the attraction of the parasitoid preferentially to lucerne or to the differential attractiveness of the aphids themselves. SAA and SCA were offered to the parasitoids in arenas of increasing complexity from single trifoliate leaves of lucerne and clover on agar through single potted plants in small cages to groups of potted plants in a large cage. Results showed that the parasitoids exhibited a preference for lucerne though, in the cage situation, they did find and parasitise SCA on clover. They did not differentiate between SAA and SCA on lucerne.     

A model of the effect of fungicides on disease-induced yield loss, for use in wheat disease management decision support systems

A model of the effect of foliar-applied fungicides on disease-induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose–response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease-induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease-induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance.