Effects of cytochalasins on developing frog embryos: protection with l-cysteine and α-d-glucosamine

Summary Cytochalasins A, B and H (CA, CB and CH) brought about cellular disaggregation and mortality in the developing embryos of the frog, Microhyla ornata. All three cytochalasins exhibited a dose-response relationship. CA was the most potent and its effects were significantly reduced by simultaneous additon of l-cysteine, a sulph-hydryl compound. -d-Glucosamine, a precursor of complex macromolecules important in cell adhesion, protected against the effects of CH. The effects of CB, however, were influenced neither by l-cysteine nor by -d-glucosamine. The results revealed differences in the mechanism of action of these three cytochalasins.     

Changes in photoelectron transport activity in cyanophage N-1-infected cells ofNostoc muscorum

Cyanophage N-1-infectedNostoc muscorum cells were unable to carry out oxygen evolution and photosystem-II-dependent electron transport (H₂ODCPIP). This was associated with preferential degradation of phycobiliproteins. Such cells also exhibited decreased rate of ferredoxin:NADP⁺ oxidoreductase activity. However, Ca²⁺-dependent ATPase activity was maintained at a higher level (80%). The results suggested that virus development proceeds in the absence of photosystem-II activity, and the energy is provided by cyclic photophosphorylation aside from that possibly obtained via degradation of carbohydrate reserves.     

Urease of blue-green algae (Cyanobacteria)Anabaena doliolum andAnacystis nidulans

Urease fromAnabaena doliolum andAnacystic nidulans showed maximum activity at pH 7.0–7.4 at 40°C when measured in cell-free, phosphate-buffered extracts. It is a soluble enzyme located in cytoplasm. The apparent K_m forA. doliolum urease was 120 M. Anacystis nidulans urease exhibited biphasic kinetics (K_m=250 M and 1.66 mM). Enzyme, fully expressed in cells grown with urea, nitrate, or N₂, was repressed in ammonia-grown cells, but ammonia did not inhibit the activity in vitro. Incubation of algal cells in N₂ medium with chloramphenicol for 12 h caused degradation of urease. Cu²⁺ at 1 M inhibited the enzyme activity by 50%, whereas Co²⁺ and Ni²⁺ up to 20 M had no effect.p-Hydroxymercuribenzoate appeared to be a more powerful inhibitor of urease than acetohydroxamic acid.Address reprint requests to: c/o Prof. Robert Tabita, Department of Microbiology, Experimental Science Building #319, The University of Texas at Austin, Austin, TX 78712, USA.     

Thermodynamic fidelity of the mammalian cytochrome P450 2B4 active site in binding substrates and inhibitors

Structural plasticity of mammalian cytochromes P450 (CYP) has recently been explored in our laboratory and elsewhere to understand the ligand-binding promiscuity. CYP2B4 exhibits very different conformations and thermodynamic signatures in binding the small inhibitor 4-(4-chlorophenyl)imidazole (4-CPI) versus the large bifonazole. Using four key active-site mutants (F296A, T302A, I363A, and V367L) that are involved in binding one or both inhibitors, we dissected the thermodynamic basis for the ability of CYP2B4 to bind substrates and inhibitors of different sizes and chemistry. In all cases, 1:1 binding stoichiometry was observed. The inhibitors 4-CPI, 1-(4-chlorophenyl)imidazole, and 1-(2-(benzyloxy)ethyl)imidazole bind to the mutants with a free energy difference (ΔΔG) of ∼ 0.5 to 1 kcal/mol compared with the wild type but with a large entropy-enthalpy compensation of up to 50 kcal/mol. The substrate testosterone binds to all four mutants with a ΔΔG of ∼ 0.5 kcal/mol but with as much as 40 kcal/mol of entropy-enthalpy compensation. In contrast, benzphetamine binding to V367L and F296A is accompanied by a ΔΔG of ∼ 1.5 and 3 kcal/mol, respectively. F296A, I363A, and V367L exhibit very different benzphetamine metabolite profiles, indicating the different substrate-binding orientations in the active site of each mutant. Overall, the findings indicate that malleability of the active site allows mammalian P450s to exhibit a high degree of thermodynamic fidelity in ligand binding.     

Evaluation of antioxidant and anticancer activities of chemical constituents of the Saururus chinensis root extracts

Evaluation of antioxidant and anticancer activities were screened by various Saururus chinensis root extracts. Four solvents (ethyl acetate, methanol, ethanol, and water) extracts were investigated for their total flavonoids, phenol contents and their antioxidant activity of DPPH (2,2-diphenyl-1-picrylhydrazyl), NO (nitric oxide), H₂O₂ (hydrogen peroxide), ABTS 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonicacid)diammonium assays, FRAP (ferric reducing ability of plasma) assays and anticancer activity. The total phenolic and flavonoid content of extracts were determined by using FC (Folin–Ciocalteu) and AlCl₃ colorimetric assay method. Total flavonoid content in these plants ranged from 24.7 to 72.1 mg g^?1 and amount of free phenolic compounds was between 11.2 and 67.1 mg g^?1 extract. The all extracts have significant levels of phenolics and flavonoids content. Anticancer activity was screened for MCF-7 breast cancer cell line. Ethanol extract shows significant of antioxidant activity and water extract shows significant of anticancer activity compared with standard (BHT) butylated hydroxy toluene. These ethanol and water extracts could be considered as a natural source for using antioxidant, and anticancer agents compared to commercial available synthetic drugs.     

Synergistic anti-inflammatory interaction between meloxicam and aminoguanidine hydrochloride in carrageenan-induced acute inflammation in rats

Interaction studies with inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) inhibitor have been conducted to assess the nature of interaction and the possible therapeutic advantage. The interaction between meloxicam--a selective COX-2 inhibitor--and aminoguanidine hydrochloride--a selective iNOS inhibitor-- was examined in carrageenan-induced paw edema in rats. Appropriate statistical method was applied to detect the nature of anti-inflammatory interaction. Different doses of meloxicam (1, 3, 10 and 30 mg/kg) or aminoguanidine hydrochloride (10, 30, 100 and 300 mg/kg) were administered orally to adult male albino rats. Higher doses of meloxicam (3, 10 and 30 mg/kg) showed statistically significant anti-inflammatory effect. However, aminoguanidine hydrochloride did not show any anti-inflammatory activity. Combination of sub-threshold dose of meloxicam (1 mg/kg) with increasing doses of aminoguanidine hydrochloride (30, 100 and 300 mg/kg) resulted in synergistic anti-inflammatory effect. Combined therapy with sub-threshold dose of aminoguanidine hydrochloride (30 mg/kg) with increasing doses of meloxicam (1, 3, 10 and 30 mg/kg) also resulted in synergistic anti-inflammatory effect. The possible mechanism of interaction could be the stimulation of COX-2 activity by nitric oxide (NO) by combining with heme component. These results suggest that co-administration of meloxicam and aminoguanidine hydrochloride may be an alternative in clinical control of inflammation.     

Induced resistance against Alternaria brassicae blight of mustard through plant extracts

An experiment was conducted to study the effect of plant extracts on soluble sugar, soluble phenol and defence-related enzymes response against Alternaria blight in mustard crop. The efficacy of six selected plant extracts (5 and 10%) used as foliar sprays at 60 and 70 days after sowing and mustard leaves was used for investigation. The results indicate that soluble phenol and sugar content in mustard leaves significantly increases in response to spraying of Azadirachta indica seed kernel, Calotropis procera and A. indica leaf extracts. The soluble protein, viz. peroxidase, polyphenol oxidase and phenylalanine ammonia lyase content, was higher in mustard leaves sprayed with C. procera leaves extract, A. indica seed kernel and Allium sativum bulb extract.     

Draft genome sequence of the nitrophenol-degrading actinomycete Rhodococcus imtechensis RKJ300

We report the 8.231-Mb genome sequence of Rhodococcus imtechensis RKJ300, isolated from pesticide-contaminated soil in Punjab, India. The genome sequence of the strain RKJ300 will be helpful in exploring the molecular pathways involved in the degradation of nitrophenols.