Compounds of Mo, V and W in biochemistry and their biomedical activity.

Molybdenum, vanadium and tungsten compounds are widely applied as analytical reagents for determination of numerous pharmacologically active substances and different biochemical parameters. Recent data from the available literature pointed to a very potent biomedical activity of compounds containing these trace elements. The present paper represents a survey on the structure and chemical properties of these compounds, as well as on their biological activity, mostly based on their interaction with cations of biomolecules, such as phospholipids and proteins. Besides, their potent inhibitory effects on cellular targets, bacterial and viral DNA and RNA polymerases will be discussed, as well. Numerous authors clearly demonstrated the antiviral (especially anti-HIV), anticoagulant and antineoplastic properties of the compounds containing the above trace elements. It has been also shown that these compounds act on some cellular enzymatic systems leading to the normalisation of blood pressure, blood glucose and serum lipid levels. Also, compounds of these trace elements represent potent antiobesity agents and express hepatoprotective and antioxidative stress activity.     

Study of degradation pathways of Amadori compounds obtained by glycation of opioid pentapeptide and related smaller fragments: stability,reactions, and spectroscopic properties

Reactions between biological amines and reducing sugars (the Maillard reaction) are among the most important of the chemical and oxidative changes occurring in biological systems that contribute to the formation of a complex family of rearranged and dehydrated covalent adducts that have been implicated in the pathogenesis of human diseases. In this study, chemistry of the Maillard reactions was studied in four model systems containing fructosamines (Amadori compounds) obtained from the endogenous opioid pentapeptide leucine-enkephalin (Tyr-Gly-Gly-Phe-Leu), leucine-enkephalin methyl ester, structurally related tripeptide (Tyr-Gly-Gly), or from amino acid (Tyr). The degradation of model compounds as well as their ability to develop Maillard fluorescence was investigated under oxidative conditions in methanol and phosphate buffer pH 7.4 at two different temperatures (37 and 70 degrees C). At 37 degrees C, glycated leucine-enkephalin degraded slowly in methanol (t(1/2) approximately 13 days) and phosphate buffer (t(1/2) approximately 9 days), producing a parent peptide compound as a major product throughout a three-week incubation period. Whereas fluorescence slowly increased over time at 37 degrees C, incubations off all studied Amadori compounds at 70 degrees C resulted in a rapid appearance of a brown color and sharp increase in AGE (advanced glycation end products)-associated fluorescence (excitation 320 nm/emmision 420 nm) as well as in distinctly higher amounts of fragmentation products. The obtained data indicated that the shorter the peptide chain the more degradation products were formed. These studies have also helped to identify a new chemical transformation of the peptide backbone in the Maillard reaction that lead to beta-scission of N-terminal tyrosine side chain and p-hydroxybenzaldehyde formation under both aqueous and nonaqueous conditions.     

Selenoprotein P in subjects exposed to mercury and other stress situations such as physical load or metal chelation treatment

In plasma, Se is found in plasma glutathione peroxidase (pGSH-Px), selenoprotein P (Sel-P), and albumins. The aim of the present study was to determine the influence of lifelong exposure to various levels of mercury vapor (Hg⁰) on plasma Se content and the fraction bound to Sel-P. Second, a pilot study was performed on the influence of short-term excessive physical stress and metal chelation (DIMAVAL) treatment. Samples of human plasma/serum obtained from a control group, Idrija residents living in a Hg-polluted environment because of the vicinity of the Idrija mercury mine (closed 1994), a few Idrija residents exposed to excessive physical stress, and two retired miners treated with the drug DIMAVAL were investigated. Selenoprotein P was isolated by affinity chromatography (heparin-Sepharose), and the concentrations of selenium were determined by radiochemical neutron activation analysis and hydride generation-atomic fluorescence spectrometry. Regardless of the group investigated, plasma Se average values were very similar (about 70–90 ngSe/g). A significant change of Sel P (7–24% decrease) was noted only in the group exposed to physical stress as compared to the same subjects before the test, to the control group, and to the Hg exposed group. The decrease of Se bound on Sel-P was accompanied by its increase in fraction of pGSH-Px with albumin.     

Mixing-models applied to industrial batch bioreactors

Mixing models for bioreactors on the basis of the tanks-in-series concept are presented and a suitable parameter-estimation method is introduced. The Monte-Carlo-optimization procedure with the inhomogeneity-curve included in the objective function is used. Results of the parameter optimization procedure are given for stirred-tank-bioreactors equipped with one and three Rushton turbines under aerated conditions. The model designed for the stirredtank with three Rushton turbines is capable to describe the mixing properties, while in case of the stirred-tank with one Rushton turbine the simulated radial circulation time does not correlate with the measured one.List of Symbols a ₀₀...a _XY coefficients in Eq. (9) - d _i m stirrer diameter - D m tank diameter - E relative error - F _AX m³/s axial liquid flow rate - F _G m³/s aeration flow rate - F _RAD m³/s radial liquid flow rate - g m/s² acceleration of gravity - h _l m height of fluid in the tank - i _s(t) simulated inhomogeneity-curve - i _m(t) measured inhomogeneity-curve - k number of sensors - n 1/s stirrer revolutions - N number of tanks in the tanks-of-series-cascade - p number of measured time intervalls - t s time - t _c.AX s axial circulation time - t _c,RAD s radial circulation time - T _i °C temperature of sensors - T °C temperature at the end of the experiment - T ₀ °C temperature before pulse injection - V _tot m³ total liquid volume - V _C m³ liquid volume of circulation cascade, additional index specifications describe the cascade elements (Figs.1 and 2) - V _M m³ liquid volume of well mixed stirrer compartment - w ₀ m/s superficial gas velocity - X, Y exponents in eq. (9) - kg/m³ density - Pas dynamic viscosity - m²/s kinematic viscosity - s time constant (time for 63,2% of T ) of the signal Dimensionless Numbers stirrer Froude number - aeration Froude number     

Is there a link between telomere maintenance and radiosensitivity?

Several recent studies point to the possibility that telomere maintenance may constitute a potential genetic marker of radiosensitivity. For example, the human diseases ataxia telangiectasia and Nijmegen breakage syndrome, which are characterized by clinical radiosensitivity, show alterations in telomere maintenance. In addition, Fanconi's anemia patients, who are characterized by mild cellular radiosensitivity and in some cases marked clinical radiosensitivity, have altered telomere maintenance. Similarly, a correlation between telomere maintenance and cellular radiosensitivity was reported in a group of breast cancer patients. Another study demonstrated that radiosensitivity may be more pronounced in human fibroblasts with short telomeres than in their counterparts with long telomeres. Several mouse models including mice deficient in Ku, DNA-PKcs (Prkdc), Parp and Atm, all of which are radiosensitive in vivo, show clear telomere alterations. The link between telomere maintenance and radiosensitivity is also apparent in mice genetically engineered to have dysfunctional telomeres. Finally, studies using non-mammalian model systems such as C. elegans and yeast point to the link between radiosensitivity and telomere maintenance. These results warrant further investigation to identify the extent to which these two phenotypes, namely radiosensitivity and telomere maintenance, are linked.     

The importance of intrinsic disorder for protein phosphorylation

Reversible protein phosphorylation provides a major regulatory mechanism in eukaryotic cells. Due to the high variability of amino acid residues flanking a relatively limited number of experimentally identified phosphorylation sites, reliable prediction of such sites still remains an important issue. Here we report the development of a new web-based tool for the prediction of protein phosphorylation sites, DISPHOS (DISorder-enhanced PHOSphorylation predictor, http://www.ist.temple. edu/DISPHOS). We observed that amino acid compositions, sequence complexity, hydrophobicity, charge and other sequence attributes of regions adjacent to phosphorylation sites are very similar to those of intrinsically disordered protein regions. Thus, DISPHOS uses position-specific amino acid frequencies and disorder information to improve the discrimination between phosphorylation and non-phosphorylation sites. Based on the estimates of phosphorylation rates in various protein categories, the outputs of DISPHOS are adjusted in order to reduce the total number of misclassified residues. When tested on an equal number of phosphorylated and non-phosphorylated residues, the accuracy of DISPHOS reaches 76% for serine, 81% for threonine and 83% for tyrosine. The significant enrichment in disorder-promoting residues surrounding phosphorylation sites together with the results obtained by applying DISPHOS to various protein functional classes and proteomes, provide strong support for the hypothesis that protein phosphorylation predominantly occurs within intrinsically disordered protein regions.     

Telomere biology: integrating chromosomal end protection with DNA damage response

Telomeres play the key protective role at chromosomes. Many studies indicate that loss of telomere function causes activation of DNA damage response. Here, we review evidence supporting interdependence between telomere maintenance and DNA damage response and present a model in which these two pathways are combined into a single mechanism for protecting chromosomal integrity. Proteins directly involved in telomere maintenance and DNA damage response include Ku, DNA-PKcs, RAD51D, PARP-2, WRN and RAD50/MRE11/NBS1 complex. Since most of these proteins participate in the repair of DNA double-strand breaks (DSBs), this was perceived by many authors as a paradox, given that telomeres function to conceal natural DNA ends from mechanisms that detect and repair DSBs. However, we argue here that the key function of one particular DSB protein, Ku, is to prevent or control access of telomerase, the enzyme that synthesises telomeric sequences, to both internal DSBs and natural chromosomal ends. This view is supported by observations that Ku has a high affinity for DNA ends; it acts as a negative regulator of telomerase and that telomerase itself can target internal DSBs. Ku then directs other DSB repair/telomere maintenance proteins to either repair DSBs at internal chromosomal sites or prevent uncontrolled elongation of telomeres by telomerase. This model eliminates the above paradox and provides a testable scenario in which the role of DSB repair proteins is to protect chromosomal integrity by balancing repair activities and telomere maintenance. In our model, a close association between telomeres and different DNA damage response factors is not an unexpected event, but rather a logical result of chromosomal integrity maintenance activities. Review related to the 15th International Chromosome Conference (ICC XV), held in September 2004, Brunel University, London, UK     

Estimation of axial dispersion in horizontal rotating tubular bioreactor by means of a structured model

A horizontal rotating tubular bioreactor (HRTB) is designed as the combination of a "thin layer bioreactor" and a "biodisc" reactor. The investigation of mixing in HRTB was done by the temperature step method in a wide range of process conditions [residence time (t_z=360036000 s) and bioreactor rotation speed (n=0.0830.917 s^у)]. In all experiments heat losses were detected. A mathematical model based on "tank in series" concept was developed to describe the mixing in HRTB - a "spiral flow" model (SFM) which has incorporated heat losses. However, the simulations of SFM could be used for calculation of temperature response curves for the case when there is no heat losses. These corrected curves were used then to estimate Bodenstein number as a parameter of standard dispersion model (SDM). The obtained Bodenstein numbers were in the range 10-17. The simulations showed that SFM was more capable to describe the mixing in HRTB giving better fitting with experimental measurements than SDM, indicating that mixing pattern in HRTB is too complex to be described with this relatively simple, one-parameter model.     

Estradiol affect Na-dependent Ca2+ efflux from synaptosomal mitochondria

The effects of gonadal steroid hormone, 17beta-estradiol (E2), in vitro on rat brain mitochondria Ca2+ movement were investigated. Intrasynaptosomal mitochondria Ca2+ uptake via an energy-driven Ca2+ uniporter have Km = 112.73 +/- 7.3 micromol x l(-1) and Vmax = 21.97 +/- 1.7 nmol 45Ca2+ mg(-1). Ca2+ release trough a Na+/Ca2+ antiporter was measured with a Km for Na+ of 43.7 +/- 2.6 mmol x l(-1), and Vmax of 1.5 +/- 0.3 nmol 45Ca2+ mg(-1). Addition of estradiol in preincubation mixture did not affect the uptake of Ca2+ mediated by the ruthenium red-sensitive uniporter, while it produced biphasic effect on Na-dependent Ca2+ efflux. Estradiol at concentrations up to 1 nmol x l(-1) decreased the efflux significantly (63% inhibition with respect to the control), and at concentrations above 10 nmol x l(-1) increased it exponentially. The maximum inhibiting concentration of estradiol (0.5 nmol x l(-1)) increased the affinity of the uniporter (Km reduced by about 30%), without affecting significantly the capacity (Vmax) for Na+. The results presented suggest that estradiol inhibits Na-dependent Ca2+ efflux from mitochondria and acts on mitochondrial retention of Ca2+, which may modulate mitochondrial and consequently synaptosomal content of Ca2+, and in this way exerts its role in the homeostasis of calcium in nerve terminals.