Mechanistic studies on the biosorption of Pb(II) by Pseudomonas aeruginosa

The biosorption of Pb(II) ions from aqueous solution has been studied using both the intact and thermolyzed cells of Pseudomonas aeruginosa. Further, the role of the major cell wall components, namely DNA, protein, polysaccharide, and lipid, in Pb(II) binding has been assessed using an enzymatic treatment method. The Pb(II) bioremediation capability of P. aeruginosa cells has been investigated by varying the parameters of pH, time of interaction, amount of biomass, and concentration of Pb(II). The complete bioremoval of Pb(II) using intact cells has been achieved for an initial Pb(II) concentration of 12.4 mg L^-1 at pH 6.2 and temperature 29 ± 1 °C. The biosorption isotherm follows Langmuirian behavior with a Gibbs free energy of -30.7 kJ mol^-1, indicative of chemisorption. The biosorption kinetics is consistent with a pseudo-second-order model. The possible Pb(II) binding mechanisms of P. aeruginosa cells are discussed based on characterization using zeta potential measurements, Fourier transform infra-red spectroscopy, and energy dispersive X-ray spectroscopy. The results confirm that among the major cell wall components studied, polysaccharide shows the highest contribution towards Pb(II) binding, followed by DNA, lipid, and protein. Similar studies using thermolyzed cells show higher Pb(II) uptake compared to the intact cells both before and after enzymatic treatment.

Probing the activity of a recombinant Zn2+ -transporting P-type ATPase

P-type ATPase proteins maintain cellular homeostasis and uphold critical concentration gradients by ATP-driven ion transport across biological membranes. Characterization of single-cycle dynamics by time-resolved X-ray scattering techniques in solution could resolve structural intermediates not amendable to for example crystallization or cryo-electron microscopy sample preparation. To pave way for such time-resolved experiments, we used biochemical activity measurements, Attenuated Total Reflectance (ATR) and time-dependent Fourier-Transform Infra-Red (FTIR) spectroscopy to identify optimal conditions for activating a Zn²⁺ -transporting Type-I ATPase from Shigella sonnei (ssZntA) at high protein concentration using caged ATP. The highest total activity was observed at a protein concentration of 25 mg/mL, at 310 K, pH 7, and required the presence of 20% (v/v) glycerol as stabilizing agent. Neither the presence of caged ATP nor increasing lipid-to-protein ratio affected the hydrolysis activity significantly. This work also paves way for characterization of recombinant metal-transporting (Type-I) ATPase mutants with medical relevance.

Controlled Release by Permeability Alteration of Cationic Ammonio Methacrylate Copolymers Using Ionic Interactions

A multiparticulate drug delivery system was studied in which the drug release of a model drug theophylline could be modulated by interactions of ammonio methacrylate polymer and anions. The system consisted of a EUDRAGIT NE coated anionic core, layered with drug and further layered with EUDRAGIT RS. The effects of different anions like chloride, succinate, citrate, and acetate as well as the thickness of the polymer layers on the in vitro drug release were studied. It was seen that succinate and acetate anions had permeability enhancing effects and citrate and chloride anions had permeability retarding effects on the polymer. The results indicate that changing these variables would enable us to get a desired release profile and hence the proposed system could be a viable alternative to existing technologies for the development of a controlled drug delivery system.

Characterization of a mouse recombination hot spot locus encoding a novel non-protein-coding RNA

Our current knowledge of recombination hot spot activity in mammalian systems implicates a role for both the primary DNA sequence and the nature of the chromatin domain around it. In mice, the only recombination hot spots mapped to date have been confined to a cluster within the major histocompatibility complex (MHC) region. We present a high resolution analysis of a new recombination hot spot in the mouse genome which maps to mouse chromosome 8 C-D. Haplotype diversity analysis across 40 different strains of mice has enabled us to map recombination breakpoints to a 1-kb interval. This hot spot has a recombination intensity that is 10- to 100-fold above the genome average and has a mean gene conversion tract length of 371 bp. This meiotically active locus happens to be flanked by a transcribed region encoding a non-protein-coding RNA polymerase II transcript and the previously characterized repair site. Many of the primary DNA sequence features that have been reported for the mouse MHC hot spots are also shared by this hot spot locus and in addition, along with three other MHC hot spot loci, we show a new parallel feature of association of the crossover sites with the nuclear matrix.

Isolation of a cytochrome P-450e gene variant and characterization of its 5' flanking sequences

A cytochrome P-450e gene variant has been isolated from the rat liver genomic library. It is a typical e gene clone but unique in having b-like single base substitutions at specific sites in the 5' flanking region. It also appears to have certain additional restriction sites in the introns. When compared with the cytochrome P-450b gene, the e gene has some of the repetitive motifs interrupted in the 5' flanking region. In addition, this region is characterized by the presence of alternating pyrimidine-purine stretch, steroid hormone regulatory elements, consensus eukaryotic enhancer sequence and sequences involved in general amino acid regulation.

Turnover of messenger RNA, apoprotein and haem of cytochrome P-450b + e induced by phenobarbitone in rat liver

A single injection of phenobarbitone elicits asynchronous behaviour in the pattern of induction of mRNA, apoprotein and haem of cytochrome P-450b + e. The mRNA content reaches a maximum around 16h, the apoprotein content reaches a maximum around 30-36h, and the holoprotein content shows biphasic behaviour, with maxima around 16h and 30-36h. With the use of CoCl2 to block fresh transcription of cytochrome P-450b + e mRNA, the half-life of the preinduced mRNA was found to be 3h. The apoprotein and haem moieties of cytochrome P-450b + e turn over with half-lives of 16h and 8h respectively. The pattern of induction of delta-aminolaevulinate synthase shows biphasic behaviour, with maxima around 16h and 30-36h. The biphasic behaviour of the holoprotein content is thus due to differences in the extent of saturation of the apoprotein with haem, the process being regulated by the activity of the rate-limiting delta-aminolaevulinate synthase and the independent faster turnover rate of haem with respect to the apoprotein. Massive degradation of the haem moiety of preformed cytochrome P-450b + e results in the subsequent degradation of the apoprotein.

Regulation of cytochrome P-450 gene expression. Studies with a cloned probe

A cDNA clone for cytochrome P-450e, a phenobarbitone-inducible species in rat liver, has been isolated and characterized. With the use of this cloned DNA, an attempt has been initiated to elucidate the factors regulating the cytochrome P-450 gene expression. Inhibitors of heme synthesis such as cobalt chloride and 3-amino-1,2,4-triazole block the induction of cytochrome P-450e by phenobarbitone at the level of transcription. This is evident from the decrease in the rate of synthesis of cytochrome P-450e, a decrease in the levels of specific translatable messenger RNA, a decrease in the specific cytoplasmic and nuclear messenger RNA contents, and nuclear transcription of cytochrome P-450e gene, as revealed by hybridization to the cloned probe, under these conditions. It is proposed that heme is a general regulator of cytochrome P-450 gene expression at the level of transcription, whereas the drug or its metabolite would impart the specificity needed for the induction of a particular species.

Effect of cobalt chloride and 3-amino-1,2,4-triazole on the induction of cytochrome P-450 synthesis by phenobarbitone in rat liver

Administration of cobalt chloride and 3-amino-1,2,4-triazole leads to a suppression of phenobarbitone-mediated increase in total cytochrome P-450 as well as cytochrome P-450b contents of the liver. This suppression is due to a decrease in the content of the protein species which is the result of a decrease in its rate of synthesis as measured in vivo and in vitro. Cobalt chloride as well as 3-amino-1,2,4-triazole treatments lead to a decrease in the translatability of cytochrome P-450b RNA without affecting total protein synthesis. It is a possibility that a small pool of heme regulates the RNA levels for the cytochrome P-450 species.