Importance of dynamical processes in the coordination chemistry and redox conversion of copper amyloid-β complexes

Interaction of Cu ions with the amyloid-β (Aβ) peptide is linked to the development of Alzheimer’s disease; hence, determining the coordination of Cu^I and Cu^II ions to Aβ and the pathway of the Cu^I(Aβ)/Cu^II(Aβ) redox conversion is of great interest. In the present report, we use the room temperature X-ray absorption near edge structure to show that the binding sites of the Cu^I and Cu^II complexes are similar to those previously determined from frozen-solution studies. More precisely, the Cu^I is coordinated by the imidazole groups of two histidine residues in a linear fashion. However, an NMR study unravels the involvement of all three histidine residues in the Cu^I binding due to dynamical exchange between several set of ligands. The presence of an equilibrium is also responsible for the complex redox process observed by cyclic voltammetry and evidenced by a concentration-dependent electrochemical response.     

Organic-matter degradative potential of Halomonas glaciei isolated from frazil ice in the Ross Sea (Antarctica)

Halomonas glaciei isolated from frazil ice in the Ross Sea (Antarctica) during austral summer 2003 was phenotypically characterized and its capability of degrading organic matter was tested. We evaluated specific bacterial growth rates (mu) to understand at which temperatures bacterial growth shows a linear and direct relationship with the available substrate (4-22 degrees C) and afterwards we tested H. glaciei growth curves and degradative potential at 0, 10 and 37 degrees C using two different media (one enriched and one depleted in PO(4)). The strain grew exponentially only at 10 degrees C. The fastest hydrolysis rates were expressed by enzymes aimed at polysaccharide degradation (alpha-d-glucosidase, beta-d-glucosidase and beta-d-galactosidase) while alkaline phosphatase and aminopeptidase activities were rather low. Our data suggest a preferential demand for carbon derived from carbohydrates rather than from proteins: ectoenzyme activities transformed into carbon mobilization from organic polymers, showed that the total carbon potentially released from polysaccharides can be almost one order of magnitude higher than the protein carbon mobilization. Principal component analysis of the enzyme affinity separated the six experimental conditions, highlighting how different physical (temperature) and chemical (PO(4) enrichment or depletion) features actively lead to a differentiation in the efficiency of the ectoenzymes produced, resulting in preferential degradation of diverse kinds of organic substrates.     

HELP LDL Apheresis Reduces Plasma Pentraxin 3 in Familial Hypercholesterolemia

Background

Pentraxin 3 (PTX3), a key component of the humoral arm of innate immunity, is secreted by vascular cells in response to injury, possibly aiming at tuning arterial activation associated with vascular damage. Severe hypercholesterolemia as in familial hypercholesterolemia (FH) promotes vascular inflammation and atherosclerosis; low-density lipoprotein (LDL) apheresis is currently the treatment of choice to reduce plasma lipids in FH. HELP LDL apheresis affects pro- and antiinflammatory biomarkers, however its effects on PTX3 levels are unknown. We assessed the impact of FH and of LDL removal by HELP apheresis on PTX3.

Methods

Plasma lipids, PTX3, and CRP were measured in 19 patients with FH undergoing chronic HELP LDL apheresis before and after treatment and in 20 control subjects. In the patients assessment of inflammation and oxidative stress markers included also plasma TNFα, fibrinogen and TBARS.

Results

At baseline, FH patients had higher (p = 0.0002) plasma PTX3 than matched control subjects. In FH PTX3 correlated positively (p≤0.05) with age, gender and CRP and negatively (p = 0.01) with HELP LDL apheresis vintage. The latter association was confirmed after correction for age, gender and CRP. HELP LDL apheresis acutely reduced (p≤0.04) plasma PTX3, CRP, fibrinogen, TBARS and lipids, but not TNFα. No association was observed between mean decrease in PTX3 and in LDL cholesterol. PTX3 paralleled lipids, oxidative stress and inflammation markers in time-course study.

Conclusion

FH is associated with increased plasma PTX3, which is acutely reduced by HELP LDL apheresis independently of LDL cholesterol, as reflected by the lack of association between change in PTX3 and in LDL levels. These results, together with the finding of a negative relationship between PTX3 and duration of treatment suggest that HELP LDL apheresis may influence both acutely and chronically cardiovascular outcomes in FH by modulating PTX3.     

A mathematical model describing the effect of temperature and substrate concentration on the activities of M4 and H4 lactate dehydrogenase from the big brown bat (Eptesicus fuscus)

The effect of temperature on the activities of M₄ and H₄ lactate dehydrogenases (LDH, EC 1.1.1.27) isolated from the big brown bat (Eptesicus fuscus) was examined. Temperature effects were dependent on the concentrations of all four LDH substrates, pyruvate, lactate, NADH, and NAD. Arrhenius plots of In v_i vs reciprocal of absolute temperature were linear for all but the lowest substrate concentrations. The slopes of these Arrhenius plots were used to calculate the temperature effect parameter (μ). Substrate-dependent temperature effects for M₄ and H₄ LDH were described by an equation for a rectangular hyperbola, $\text{μ =}\text{[E}{}_{\mathrm{\beta }}\text{S + E}{}_{\mathrm{\alpha }}\text{K}{}_{\mathrm{t}}\text{]}\text{[K}{}_{\mathrm{t}}\text{+ S]}$ proposed by G. R. Harbison and J. R. Fisher (1974, Comp. Biochem. Physiol.47B, 27–32) for adenosine deaminase. The parameters E_α (μ at infinitely low substrate concentration), E_β (μ at infinitely high substrate concentration), and K_t (the concentration of substrate when $\text{μ =}\text{[E}{}_{\mathrm{\alpha }}\text{+ E}{}_{\mathrm{\beta }}\text{]}\text{2}$) can be used to describe the temperature dependence of LDH activity at any substrate concentration and to compare the substrate-dependent temperature effects on the two isoenzymes. Significantly different E_β and K_t values for pyruvate-dependent temperature effects and different E_β, E_α, K_t, and E_β ? E_α (the range of possible μ values) for lactate-dependent temperature effects were found between M₄ and H₄ LDH isoenzymes. High lactate concentrations inhibited bat H₄ LDH activity to a greater degree at low temperatures than at high temperatures. Thus substrate inhibition plays an important role in the effect of temperature on the activity of H-type LDH at high lactate concentrations. Substrate-dependent temperature effects on bat LDH activity were the result of temperature effects on the apparent K_m value of the respective substrate. Since both the apparent K_m for pyruvate and the K_i for the competitive inhibitor oxamate decreased with decreasing temperature, the substrate-dependent temperature effects observed for pyruvate probably resulted from an increased affinity between pyruvate and the LDH-NADH complex with decreasing temperature.     

Purification and characterization of vitamin B6-phosphate phosphatase from human erythrocytes.

Human erythrocytes rapidly convert vitamin B6 to pyridoxal-P and contain soluble phosphatase activity which dephosphorylates pyridoxal-P at a pH optimum of 6-6.5. This phosphatase was purified 51,000-fold with a yield of 39% by ammonium sulfate precipitation and chromatography on DEAE-Sepharose, Sephacryl S-200, hydroxylapatite, and reactive yellow 86-agarose. Sephacryl S-200 chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the enzyme was a dimer with a molecular mass of approximately 64 kDa. The phosphatase required Mg2+ for activity. It specifically catalyzed the removal of phosphate from pyridoxal-P, pyridoxine-P, pyridoxamine-P, 4-pyridoxic acid-P, and 4-deoxypyridoxine-P at pH 7.4. Nucleotide phosphates, phosphoamino acids, and other phosphorylated compounds were not hydrolyzed significantly nor were they effective inhibitors of the enzyme. The phosphatase showed Michaelis-Menten kinetics with its substrates. It had a Km of 1.5 microM and a Vmax of 3.2 mumol/min/mg with pyridoxal-P. The Vmax/Km was greatest with pyridoxal-P greater than 4-pyridoxic acid-P greater than pyridoxine-P greater than pyridoxamine-P. The phosphatase was competitively inhibited by the product, inorganic phosphate, with a Ki of 0.8 mM, and weakly inhibited by pyridoxal. It was also inhibited by Zn2+, fluoride, molybdate, and EDTA, but was not inhibited by levamisole, L-phenylalanine, or L(+)-tartrate. These properties of the purified enzyme suggest that it is a unique acid phosphatase that specifically dephosphorylates vitamin B6-phosphates.     

Seasonal variations in carbon and nitrogen content of Acartia clausi (Copepoda,Calanoida) in the Gulf of Trieste (Northern Adriatic Sea)

A yearly study was made on total and cephalothorax lengths, dry weight, carbon and nitrogen contents and C:N ratio of the species Acartia clausi (Copepoda, Calanoida) which is always abundant, particularly in spring, in the net zooplankton community of the Gulf of Trieste (Northern Adriatic Sea). The samples of net zooplankton were carried out every month at the permanent station located 200 m offshore and preserved for about one year in 4% buffered formalin to insure weight loss stabilization. A. clausi was separated from other zooplankton specimens; washed and dried. For each monthly sample the average total and cephalothorax lengths and the average dry weight of adult organisms of A. clausi were measured. The mean carbon and nitrogen contents, as a percentage of dry weight, were determined by using a CHN analyser. Linear regression models were computed on the log-transformed data in order to check the relationships between dry weight, total and cephalothorax lengths, carbon and nitrogen contents and C:N ratio of A. clausi. The best of the various established correlations, was between dry weight and carbon content. Our study pinpointed a high seasonal variability of the C:N ratio, mainly due to seasonal fluctuations in the nitrogen content.     

PALM THORN INJURIES—Difficulty in Diagnosis of Late Sequelae

Injuries in which palm thorns become embedded in soft tissues or cartilage, leaving no external evidence of their presence, sometimes present a baffling diagnostic problem. A high index of suspicion is the most important aid in diagnosis. Laboratory findings are not helpful and rarely can conclusive diagnosis be made from clinical examination. Surgical excision of the buried thorn is the only satisfactory treatment.     

Biodiversity of settled material in a sediment trap in the Gulf of Trieste (northern Adriatic Sea)

Phytoplankton succession and sinking rates were studied from January to December 2003 at a coastal station in the Gulf of Trieste (northern Adriatic Sea), 200 m offshore, in a relatively undisturbed area. A conical sediment trap, moored at 15 m depth (water depth 17 m), was used. The hypothesis if the presence of benthic and epiphytic diatoms can lead to an overestimation of the vertical fluxes was tested. To evaluate primary and secondary sedimentation contributions, planktonic, benthic and epiphytic diatoms were distinguished. Benthic species abundance varied throughout the year and it was related to resuspension that strongly influenced sinking rates. All over the year, diatoms were the prevailing class in the trap material accounting for 75.32% of the settled cells, while flagellates represented 24.11%. Dinophyceae and resting cells constituted minor components, accounting for 0.43% and 0.14%, respectively. The gross sedimentation rates ranged from 0.006 × 10⁸ cell m⁻² d⁻¹ in the second week of May to 6.30 × 10⁸ cell m⁻² d⁻¹ in the third week of January with a mean annual value of 1.09 ± 1.43 × 10⁸ cell m⁻² d⁻¹. To the primary sedimentation rate Pseudo-nitzschia seriata of the group “Nitzschia seriata complex” contributed for 49.77% followed by Chaetoceros spp. (23.88%). The major contributor to the secondary sedimentation rate was the diatom Paralia sulcata, accounting for 24.76%. Epiphytic diatoms contributed for 11.19% and 12.27% on annual average gross abundance and biomass, respectively, reaching even 72.04% of gross abundance and 56.06% of gross biomass in the second week of August. The correlation between temperature and the logarithm of the epiphytic biomass was statistically significant, with r = 0.66 and P < 0.001. Both in the cluster analysis and in the PCA four main groups were formed, where benthic and epiphytic species were separately gathered. Planktonic, benthic and epiphytic forms accounted for 50.78%, 36.95% and 12.27%, respectively, calculated on the annual average biomass. Therefore, vertical fluxes can be overestimated of 50% or more if benthic and epiphytic species are not rejected.     

Conserved Cysteines of the Human Immunodeficiency Virus Type 1 Protease Are Involved in Regulation of Polyprotein Processing and Viral Maturation of Immature Virions

We investigated the role of the two highly conserved cysteine residues, cysteines 67 and 95, of the human immunodeficiency virus type 1 (HIV-1) protease in regulating the activity of that protease during viral maturation. To this end, we generated four HIV-1 molecular clones: the wild type, containing both cysteine residues; a protease mutant in which the cysteine at position 67 was replaced by an alanine (C67A); a C95A protease mutant; and a double mutant (C67A C95A). When immature virions were produced in the presence of an HIV-1 protease inhibitor, KNI-272, and the inhibitor was later removed, limited polyprotein processing was observed for wild-type virion preparations over a 20-h period. Treatment of immature wild-type virions with the reducing agent dithiothreitol considerably improved the rate and extent of Gag processing, suggesting that the protease is, in part, reversibly inactivated by oxidation of the cysteine residues. In support of this, C67A C95A virions processed Gag up to fivefold faster than wild-type virions in the absence of a reducing agent. Furthermore, oxidizing agents, such as H₂O₂ and diamide, inhibited Gag processing of wild-type virions, and this effect was dependent on the presence of cysteine 95. Electron microscopy revealed that a greater percentage of double-mutant virions than wild-type virions developed a mature-like morphology on removal of the inhibitor. These studies provide evidence that under normal culture conditions the cysteines of the HIV-1 protease are susceptible to oxidation during viral maturation, thus preventing immature virions from undergoing complete processing following their release. This is consistent with the cysteines being involved in the regulation of viral maturation in cells under oxidative stress.     

Structure of integrin, a glycoprotein involved in the transmembrane linkage between fibronectin and actin

We describe the isolation, characterization, and sequence of cDNA clones encoding one subunit of the complex of membrane glycoproteins that forms part of the transmembrane connection between the extracellular matrix and the cytoskeleton. The cDNA sequence encodes a polypeptide of 89 kd that has features strongly suggesting the presence of a large N-terminal extracellular domain, a single transmembrane segment, and a small C-terminal cytoplasmic domain. The extracellular domain contains a threefold repeat of a novel 40 residue cysteine-rich segment, and the cytoplasmic domain contains a tyrosine residue that is a potential site for phosphorylation by tyrosine kinases. We propose the name integrin for this protein complex to denote its role as an integral membrane complex involved in the transmembrane association between the extracellular matrix and the cytoskeleton.