Arsenic co-exposure potentiates benzo[a]pyrene genotoxicity

The reactive industrial chemicals acrylamide (AA) and N-methylolacrylamide (MAA) are neurotoxic and carcinogenic in animals, MAA showing a lower potency than AA. The causative agent in AA-induced carcinogenesis is assumed to be the epoxy metabolite, glycidamide (GA), which in contrast to AA gives rise to stable adducts to DNA. The causative agent in MAA induced carcinogenesis is so far not studied. The two AAs were studied in mice and rats using analysis of hemoglobin (Hb) adducts as a measure of in vivo doses and the in vivo micronucleus (MN) assay as an end-point for chromosome damage. Male CBA mice were treated by intraperitoneal (i.p.) injection of three different doses and male Sprague-Dawley rats with one dose of each AA. Identical adducts were monitored from the two AAs [N-(2-carbamoylethyl)valine] and the respective epoxide metabolites [N-(2-carbamoyl-2-hydroxyethyl)valine]. Per unit of administered amount, AA gives rise to higher (three to six times) Hb adduct levels than MAA in mice and rats. Mice exhibit, compared with rats, higher in vivo doses of the epoxy metabolites, indicating that AAs were more efficiently metabolized in the mice. In mouse the two AAs induced dose-dependent increases in both Hb adduct level and MN frequency in peripheral erythrocytes. Per unit of administered dose MAA showed only half the potency for inducing micronuclei compared with AA, although the MN frequency per unit of in vivo dose of measured epoxy metabolite was three times higher for MAA than for AA. No increase in MN frequency was observed in rat bone marrow erythrocytes, after treatment with either AA. This is compatible with a lower sensitivity of the rat than of the mouse to the carcinogenic action of these compounds.     

Genetic analysis of functions involved in the late stages of biofilm development in Burkholderia cepacia H111

Burkholderia cepacia and Pseudomonas aeruginosa often co-exist as mixed biofilms in the lungs of patients suffering from cystic fibrosis (CF). Here, we report the isolation of 13 random mini-Tn5 insertion mutants of B. cepacia H111 that are defective in biofilm formation on a polystyrene surface. We show that the screening procedure used in this study is biased towards mutants defective in the late stages of biofilm development. A detailed quantitative analysis of the biofilm structures formed by wild-type and mutant strains revealed that the isolated mutants are impaired in their abilities to develop a typical three-dimensional biofilm structure. Molecular investigations showed that the genes required for biofilm maturation fall into several classes: (i). genes encoding for surface proteins; (ii). genes involved in the biogenesis and maintenance of an integral outer membrane; and (iii). genes encoding regulatory factors. It is shown that three of the regulatory mutants produce greatly reduced amounts of N-octanoylhomoserine lactone (C8-HSL). This compound serves as the major signal molecule of the cep quorum-sensing system. As this density-dependent regulatory system is involved in the regulation of biofilm maturation, we investigated the interplay between the three regulatory genes and the quorum-sensing cascade. The results of these investigations show that the identified genes encode for regulatory elements that are positioned upstream of the cep system, indicating that the quorum-sensing system of B. cepacia is a major checkpoint for biofilm formation.     

Vomilenine reductase--a novel enzyme catalyzing a crucial step in the biosynthesis of the therapeutically applied antiarrhythmic alkaloid ajmaline

Delineation of the biochemical pathway leading to the antiarrhythmic Rauvolfia alkaloid ajmaline has been an important target in biosynthetic research for many years. The biosynthetic sequence starting with tryptamine and the monoterpene secologanin consists of about 10 different steps. Most of the participating enzymes have been detected and characterized previously, except those catalyzing the reduction of the intermediate vomilenine. A novel NADPH-dependent enzyme that reduces the intermediate has been isolated from Rauvolfia serpentina cell suspension cultures. Vomilenine reductase (M(r )43 kDa, temp opt 30 degrees C, pH opt 5.7-6.2), saturates the indolenine double bond of vomilenine with stereospecific formation of 2beta(R)-1,2-dihydrovomilenine. The described detection, enrichment and properties of the reductase not only closes a gap in ajmaline biosynthesis but is also a prerequisite for overexpressing the protein heterologously for final clarification of its molecular properties.     

Biphasic oxygen kinetics of cellular respiration and linear oxygen dependence of antimycin A inhibited oxygen consumption

Oxygen kinetics in fibroblasts was biphasic. This was quantitatively explained by a major mitochondrial hyperbolic component in the low-oxygen range and a linear increase of rotenone-and antimycin A-inhibited oxygen consumption in the high-oxygen range. This suggests an increased production of reactive oxygen species and oxidative stress at elevated, air-level oxygen concentrations. The high oxygen affinity of mitochondrial respiration provides the basis for the maintenance of a high aerobic scope at physiological low-oxygen levels, whereas further pronounced depression of oxygen pressure induces energetic stress under hypoxia.