Repurposing the Pummerer Rearrangement: Determination of Methionine Sulfoxides in Peptides

The reversible oxidation of methionine residues in proteins has emerged as a biologically important post-translational modification. However, detection and quantitation of methionine sulfoxide in proteins is difficult. Our aim is to develop a method for specifically derivatizing methionine sulfoxide residues. We report a Pummerer rearrangement of methionine sulfoxide treated sequentially with trimethylsilyl chloride and then 2-mercaptoimidazole or pyridine-2-thiol to produce a dithioacetal product. This derivative is stable to standard mass spectrometry conditions, and its formation identified oxidized methionine residues. The scope and requirements of dithioacetal formation are reported for methionine sulfoxide and model substrates. The reaction intermediates have been investigated by computational techniques and by ¹³C NMR spectroscopy. These provide evidence for an α-chlorinated intermediate. The derivatization allows for detection and quantitation of methionine sulfoxide in proteins by mass spectrometry and potentially by immunochemical methods.     

Influence of non-inherited maternal HLA-DR antigens on susceptibility to rheumatoid arthritis

OBJECTIVE: It has recently been observed that non-inherited maternal DR4 antigens (NIMAs) of DR4 negative rheumatoid arthritis (RA) patients were increased compared with non-inherited paternal DR4 antigens (NIPAs). The aim of this study was to determine the prevalence of non-inherited DR4 antigens and DRB1 alleles in parents of RA patients. METHODS: HLA-DR serology and DRB1 typing was performed in 97 RA patients and their parents. NIMA and NIPA frequencies were compared, stratified according to the presence of DR4 and/or the shared epitope (SE). RESULTS: In DR4 negative patients, NIMA DR4 was increased compared with NIPA DR4 (OR 3.10, 95% CI 0.76, 12.70). When combined with results from a previous study this increase was significant (OR 3.65, 95% CI 1.29, 10.31). The NIMA effect of SE positive DR4 subtypes in this study (OR 4.73, 95% CI 0.94, 23.8) was stronger than the NIMA effect of combined SE positive DRB1 alleles (OR 2.19 95% CI 0.36, 13.22). CONCLUSIONS: The association between non-inherited maternal HLA-DR4 alleles and the susceptibility to RA was observed in two independent populations.     

Effect of polymerization temperature and time on the residual monomer content of denture base polymers

The aim of this study was to investigate the effect of polymerization time and polymerization temperature on the residual methyl methacrylate (MMA) content of two heat-cured and two autopolymerized denture base polymers. Gas chromatography was used to determine the residual MMA content of three test specimens of each type of polymer. Increasing the polymerization temperature for the autopolymerized denture base resins from 30 degrees C to 60 degrees C decreased the residual MMA content of the polymer from an average of 4.6 wt% to 3.3 wt%. With the heat-cured denture base resins, a curing cycle at a polymerization temperature of 70 degrees C followed by a period at 100 degrees C significantly reduced the residual monomer content of the polymer when compared with a resin cured at 70 degrees C only. Polymerizing the heat-cured denture base resin at 100 degrees C only for various lengths of time significantly affected the residual MMA content of the polymer. The lowest residual MMA content (0.07 wt%) was obtained by polymerizing the heat-cured denture base resin at 100 degrees C for 12 h. The results of this study suggest that the polymerization temperature and polymerization time considerably affect the residual MMA content of denture base polymers.     

N-methyl-D-aspartic acid stimulation of vasopressin release: role in osmotic regulation and modulation by gonadal steroids

Previous experiments demonstrated that excitatory amino acids participate in the osmotic regulation of vasopressin secretion, but the specific involvement of N-methyl-D-aspartic acid (NMDA) receptors was not evaluated. This was demonstrated in the present studies. NMDA stimulated vasopressin release from perifused explants of the hypothalamo-neurohypophyseal system (HNS), and osmotic stimulation of vasopressin release was inhibited by MK-801 (10 microM) and AP5 (100 microM) NMDA receptor antagonists. The effective concentration of NMDA was dependent upon the Mg2+ concentration of the perifusate with stimulation observed at 1 microM NMDA in Mg2+-replete compared with 5 microM in low-Mg2+ medium. Previous experiments also demonstrated that estradiol and dihydrotestosterone (DHT) inhibited osmotically stimulated vasopressin secretion, and a nongenomic mechanism of action was suggested by the ability of steroids conjugated to bovine serum albumin to replicate the effect. Experiments were performed to explore the potential role of NMDA receptors in this mechanism. Estradiol (50 pg/ml) and DHT (3 ng/ml) inhibited NMDA stimulated vasopressin release in perifused HNS explants. These results suggest a role of NMDA receptors in the mediation of vasopressin secretion in osmotically stimulated release. Furthermore, estradiol and DHT may exert their inhibitory effect on osmotically stimulated vasopressin release via the NMDA receptor.     

Ichthyodeterrent Properties of Lipophilic Extracts from Bermudian Sponges

The feeding deterrent properties of hexane, ethyl acetate, and butanol lipophilic extracts of 16 species of Bermudian sponges presented to the sergeant major,Abudefduf saxatilus, and the Bermuda bream,Diplodus bermudensis, were investigated in the laboratory. The sponges investigated spanned a variety of different color morphs and were representative of patch reef, mangrove, rock wall, soft bottom, seagrass, and cave habitats. Six of the 16 sponges (36%) had at least one extract that deterred feeding byA. saxatilus, while only one of 16 sponges (6%) had an extract that deterred feeding byD. bermudensis. Among those sponges that deterred feeding in one or both fish, deterrence was most frequently associated with compounds extracted in ethyl acetate (moderately polar). Butanol extracts (most polar) were active in only half as many instances, while in only one case was a hexane extract (least polar) active. Both brighly colored (yellow, orange–yellow, gray–blue, purple–brown) and weakly colored (dull brown, pinkish white) sponges had hexane, ethyl acetate, or butanol extracts that were deterrent. Generally the numbers of sponges with bioactive lipophilic extracts that caused feeding deterrence in fish was low. This may be related to Bermuda being located just within or beyond the extreme northern range of many tropical fish and invertebrates, and therefore sponges are exposed to reduced levels of predation.     

Pervaporative desalination of water using natural zeolite membranes

Several deposits of dense natural clinoptilolite, including one from British Columbia, Canada, have been identified which exhibit both high zeolite content and essentially no macroporosity or intercrystalline voids. Sections of zeolite mineral from the British Columbia deposit were machined into thin membranes and used in the pervaporative desalination of water samples with varying salinity levels, including synthetic seawater. Essentially complete rejection of Mg²⁺ and Ca²⁺ (99.99% and 98.52%) and high levels of rejection of Na⁺ and K⁺ (over 97.5%) were observed when using a synthetic seawater feed at 75 °C and 1 atm feed-side pressure. Water flux through the natural zeolite membranes was dependent on the ion concentration in the feed, the operating temperature and the feed salinity. At 93 °C, water fluxes of 2.5 kg/m²·h and 0.39 kg/m²·h were obtained for feed concentrations of 100 mg/L Na⁺ and 5500 mg/L Na⁺, respectively. The high ion rejection and water flux observed for these rugged and economical natural clinoptilolite membranes indicates their potential utility for desalination applications.     

Effects of Ingredients on the Functionality of Fat-free Process Cheese Spreads

Emulsifying salts and hydrocolloids, cook time, cook temperature, and pH were evaluated to characterize their effects on firmness, meltability, and spreadability of fat‐free process‐cheese spreads. Disodium phosphate and trisodium citrate produced properties closest to those of a full‐fat reference cheese, with trisodium citrate providing the most meltability. In all cases, incorporation of hydrocolloids resulted in increased firmness, decreased melt, with varying results on spreadability. Increases in cook time generally produced softer, more meltable cheeses, while increases in cook temperature decreased firmness and increased meltability and spreadability.     

The Conditions for Se-Enzymes,NO, cGMP and LDL to be Formed and How They are Connected with Each Other

Transportation of energy and substances is fundamental for the conditions of life. The energy from metabolised food is yielded at the reduction of oxygen by the assistance of Se-enzymes. Activated Se-enzymes contain an electron conducting Se-link with elemental Se bounded to Se-cys （Se-cystein） that prevents electron transferring （autoxidable） agents, as arginine, from oxidations. NO is formed from e.g. arginine during the passive state of a Se-enzyme. With NO, instead of O2, bounded to a hem group, destroying oxidations are avoided. This is the role of NO. A nerve signal is activated by the GTP （guanosine triphosphate）-induced triggered transformation of cGMP （cyclic guanosine monophosphate） into GMP, closing the sodium channels. When GTP is consumed, the opposite reaction takes place. The direct influence of the GMP/cGMP quote on a nerve signal makes GMP/cGMP equal to EDHF （endothelium-derived hyperpolarizing factor）. Part of the energy from food is stored and transported in the form of acetyl groups, building up many important molecules of which LDL （low density lipoprotein） is one, containing cholesteryl esters. These are brought in to the cell, decomposed to acetyl groups generating hydrogen, H, making LDL to an essential substance. High levels are connected to impaired energy yielding reactions, perhaps related to low levels of some substances, especially to one or both forms of Se. The necessity of a Se-link and NO induced protection against oxidations by reducible oxygen can no longer be neglected.