Inhibitory effect of sulfur-containing compounds in Scorodocarpus borneensis Becc. on the aggregation of rabbit platelets.
The inhibitory effects of three pure compounds isolated from wood garlic, 2,4,5-trithiahexane (I), 2,4,5,7-tetrathiaoctane (II), and 2,4,5,7-tetrathiaoctane 2,2-dioxide (III), on rabbit platelet aggregation induced by collagen, arachidonic acid, U46619, ADP (adenosine 5'-diphosphate), PAF (platelet aggregating factor), and thrombin were studied in vitro. The anti-aggregating activity of 2,4,5,7-tetrathiaoctane 4,4-dioxide (IV) was also measured with collagen and arachidonic acid. I, II, III, and IV inhibited the platelet aggregation induced by all tested agonists. I, II, and III exhibited a stronger inhibitory effect against the thrombin-induced aggregation of GFP (gel-filtered platelets) than against the aggregation induced by the other agonists. Notably, the IC50 value for III was 4 microM, which is approximately 2.5 times stronger than MATS (methyl allyl trisulfide), a major anti-platelet compound isolated from garlic. In inhibiting collagen-induced aggregation, II was as potent as MATS and aspirin, with a marked disaggregation effect on the secondary aggregation by arachidonic acid, at the rate of 47.05%/min at a concentration of 10(-4) M. I, II, and III also suppressed U46619-induced aggregation. These results suggest that sulfur-containing compounds in wood garlic not only inhibit arachidonic acid metabolism but also suppress aggregation in association with the function of the platelet plasma membrane. (+info)
DNA conformational dynamics in the presence of catanionic mixtures.
DNA conformational behavior in the presence of non-stoichiometric mixtures of two oppositely charged surfactants, cetyltrimethylammonium bromide and sodium octyl sulfate, was directly visualized in an aqueous solution with the use of a fluorescence microscopy technique. It was found that in the presence of cationic-rich catanionic mixtures, DNA molecules exhibit a conformational transition from elongated coil to compact globule states. Moreover, if the catanionic mixtures form positively charged vesicles, DNA is adsorbed onto the surface of the vesicles in a collapsed globular form. When anionic-rich catanionic mixtures are present in the solution, no change in the DNA conformational behavior was detected. Cryogenic transmission electron microscopy, as well as measurements of translational diffusion coefficients of individual DNA chains, supported our optical microscopy observations. (+info)
Biotransformation and male rat-specific renal toxicity of diethyl ethyl- and dimethyl methylphosphonate.
Dimethyl methylphosphonate (DMMP) is a widely used chemical. Diethyl ethylphosphonate (DEEP) has been proposed as a replacement for DMMP in several applications. A long-term carcinogenesis study with DMMP in rats and mice showed a significant increase in the incidence of kidney tumors after 2 years of exposure in male but not in female rats and both sexes of mice. DMMP is not genotoxic. Due to these findings, a role of alpha(2u)-globulin accumulation in organ-specific tumorigenicity may be possible. alpha(2u)-Globulin is a low-molecular-weight protein synthesized in male rats under androgen control. Several male rat specific renal carcinogens have been shown to bind to alpha(2u)-globulin and to impair the renal degradation of this protein. This impairment results in alpha(2u)-globulin accumulation in the kidney, lysosomal overload, cell death, cell proliferation, and finally, renal tumor induction. To further characterize the toxicology of DMMP and DEEP, we investigated the biotransformation of these compounds and their ability to induce alpha(2u)-globulin accumulation in kidney. Biotransformation of both DMMP and DEEP were studied in male and female rats after single oral doses of 50 and 100 mg/kg. 31P-NMR and GC/MS showed that unchanged DMMP was excreted with urine; methyl phosphonate was identified as the only metabolite in urine. Unchanged DEEP was also excreted with urine; in addition, ethyl ethylphosphonate and ethylphosphonate were urinary metabolites. The majority of the applied dose of both compounds was recovered in urine within 24 h indicating rapid absorption and excretion. No sex-differences in rates of formation or excretion of metabolites were seen. To investigate alpha(2u)-globulin accumulation in the kidney after DMMP and DEEP, male and female Fischer-344 rats were administered DMMP or DEEP daily for five consecutive days by gavage. DMMP doses were 500- and 1,000-mg/kg body weight (bw); due to marked toxicity, daily DEEP dose of 50 and 100 mg/kg had to be used. Control rats received corn oil only and positive controls received five doses of 500-mg/kg bw trimethylpentane (TMP). Relative kidney weights were increased in male rats dosed with DMMP, DEEP, and TMP. alpha(2u)-Globulin in kidney cytosol was separated and quantified by capillary electrophoresis and by SDS-PAGE and Western blotting. In DMMP-, DEEP-, and TMP-treated rats, dose-dependent increases in the alpha(2u)-globulin content were observed by both methods in male, but not female rats. The increase of alpha(2u)-globulin accumulation was accompanied by the formation of protein droplets in the proximal tubules of male rats. These data demonstrate that the sex specific increase in kidney tumors by DMMP in male rats may be due to alpha(2u)-globulin accumulation and that similar toxic effects are to be expected from DEEP. (+info)
Peptide interfacial adsorption is kinetically limited by the thermodynamic stability of self association.
We present a study of the adsorption of two peptides at the octane-water interface. The first peptide, Lac21, exists in mixed monomer-tetramer equilibrium in bulk solution with an appreciable monomer concentration. The second peptide, Lac28, exists as a tetramer in solution, with minimal exposed hydrophobic surface. A kinetic limitation to interfacial adsorption exists for Lac28 at moderate to high surface coverage that is not observed for Lac21. We estimate the potential energy barrier for Lac28 adsorption to be 42 kJ/mol and show that this is comparable to the expected free energy barrier for tetramer dissociation. This finding suggests that, at moderate to high surface coverage, adsorption is kinetically limited by the availability of interfacially active monomeric "domains" in the subinterfacial region. We also show how the commonly used empirical equation for protein adsorption dynamics can be used to estimate the potential energy barrier for adsorption. Such an approach is shown to be consistent with a formal description of diffusion-adsorption, provided a large potential energy barrier exists. This work demonstrates that the dynamics of interfacial adsorption depend on protein thermodynamic stability, and hence structure, in a quantifiable way. (+info)
A Mycobacterium strain with extended capacities for degradation of gasoline hydrocarbons.
A bacterial strain (strain IFP 2173) was selected from a gasoline-polluted aquifer on the basis of its capacity to use 2,2, 4-trimethylpentane (isooctane) as a sole carbon and energy source. This isolate, the first isolate with this capacity to be characterized, was identified by 16S ribosomal DNA analysis, and 100% sequence identity with a reference strain of Mycobacterium austroafricanum was found. Mycobacterium sp. strain IFP 2173 used an unusually wide spectrum of hydrocarbons as growth substrates, including n-alkanes and multimethyl-substituted isoalkanes with chains ranging from 5 to 16 carbon atoms long, as well as substituted monoaromatic hydrocarbons. It also attacked ethers, such as methyl t-butyl ether. During growth on gasoline, it degraded 86% of the substrate. Our results indicated that strain IFP 2173 was capable of degrading 3-methyl groups, possibly by a carboxylation and deacetylation mechanism. Evidence that it attacked the quaternary carbon atom structure by an as-yet-undefined mechanism during growth on 2,2,4-trimethylpentane and 2,2-dimethylpentane was also obtained. (+info)
Screening of genes involved in isooctane tolerance in Saccharomyces cerevisiae by using mRNA differential display.
A Saccharomyces cerevisiae strain, KK-211, isolated by the long-term bioprocess of stereoselective reduction in isooctane, showed extremely high tolerance to the solvent, which is toxic to yeast cells, but, in comparison with its wild-type parent, DY-1, showed low tolerance to hydrophilic organic solvents, such as dimethyl sulfoxide and ethanol. In order to detect the isooctane tolerance-associated genes, mRNA differential display (DD) was employed using mRNAs isolated from strains DY-1 and KK-211 cultivated without isooctane, and from strain KK-211 cultivated with isooctane. Thirty genes were identified as being differentially expressed in these three types of cells and were classified into three groups according to their expression patterns. These patterns were further confirmed and quantified by Northern blot analysis. On the DD fingerprints, the expression of 14 genes, including MUQ1, PRY2, HAC1, AGT1, GAC1, and ICT1 (YLR099c) was induced, while the expression of the remaining 16 genes, including JEN1, PRY1, PRY3, and KRE1, was decreased, in strain KK-211 cultivated with isooctane. The genes represented by HAC1, PRY1, and ICT1 have been reported to be associated with cell stress, and AGT1 and GAC1 have been reported to be involved in the uptake of trehalose and the production of glycogen, respectively. MUQ1 and KRE1, encoding proteins associated with cell surface maintenance, were also detected. Based on these results, we concluded that alteration of expression levels of multiple genes, not of a single gene, might be the critical determinant for isooctane tolerance in strain KK-211. (+info)
Voltage-dependent insertion of alamethicin at phospholipid/water and octane/water interfaces.
Understanding the binding and insertion of peptides in lipid bilayers is a prerequisite for understanding phenomena such as antimicrobial activity and membrane-protein folding. We describe molecular dynamics simulations of the antimicrobial peptide alamethicin in lipid/water and octane/water environments, taking into account an external electric field to mimic the membrane potential. At cis-positive potentials, alamethicin does not insert into a phospholipid bilayer in 10 ns of simulation, due to the slow dynamics of the peptide and lipids. However, in octane N-terminal insertion occurs at field strengths from 0.33 V/nm and higher, in simulations of up to 100 ns duration. Insertion of alamethicin occurs in two steps, corresponding to desolvation of the Gln7 side chain, and the backbone of Aib10 and Gly11. The proline induced helix kink angle does not change significantly during insertion. Polyalanine and alamethicin form stable helices both when inserted in octane and at the water/octane interface, where they partition in the same location. In water, both polyalanine and alamethicin partially unfold in multiple simulations. We present a detailed analysis of the insertion of alamethicin into the octane slab and the influence of the external field on the peptide structure. Our findings give new insight into the mechanism of channel formation by alamethicin and the structure and dynamics of membrane-associated helices. (+info)
Rubredoxins involved in alkane oxidation.
Rubredoxins (Rds) are essential electron transfer components of bacterial membrane-bound alkane hydroxylase systems. Several Rd genes associated with alkane hydroxylase or Rd reductase genes were cloned from gram-positive and gram-negative organisms able to grow on n-alkanes (Alk-Rds). Complementation tests in an Escherichia coli recombinant containing all Pseudomonas putida GPo1 genes necessary for growth on alkanes except Rd 2 (AlkG) and sequence comparisons showed that the Alk-Rds can be divided in AlkG1- and AlkG2-type Rds. All alkane-degrading strains contain AlkG2-type Rds, which are able to replace the GPo1 Rd 2 in n-octane hydroxylation. Most strains also contain AlkG1-type Rds, which do not complement the deletion mutant but are highly conserved among gram-positive and gram-negative bacteria. Common to most Rds are the two iron-binding CXXCG motifs. All Alk-Rds possess four negatively charged residues that are not conserved in other Rds. The AlkG1-type Rds can be distinguished from the AlkG2-type Rds by the insertion of an arginine downstream of the second CXXCG motif. In addition, the glycines in the two CXXCG motifs are usually replaced by other amino acids. Mutagenesis of residues conserved in either the AlkG1- or the AlkG2-type Rds, but not between both types, shows that AlkG1 is unable to transfer electrons to the alkane hydroxylase mainly due to the insertion of the arginine, whereas the exchange of the glycines in the two CXXCG motifs only has a limited effect. (+info)