Kinetics and thermodynamics of catalysis and thermal inactivation of a novel α-amylase (Tp-AmyS) from Thermotoga petrophila

Abstract

This research is focussed on kinetic, thermodynamic and thermal inactivation of a novel thermostable recombinant α-amylase (Tp-AmyS) from Thermotoga petrophila. The amylase gene was cloned in pHIS-parallel1 expression vector and overexpressed in Escherichia coli. The steady-state kinetic parameters (V_max, K_m, k_cat and k_cat/K_m) for the hydrolysis of amylose (1.39?mg/min, 0.57?mg, 148.6?s^?1, 260.7), amylopectin (2.3?mg/min, 1.09?mg, 247.1?s^?1, 226.7), soluble starch (2.67?mg/min, 2.98?mg, 284.2?s^?1, 95.4) and raw starch (2.1?mg/min, 3.6?mg, 224.7?s^?1, 61.9) were determined. The activation energy (E_a), free energy (ΔG), enthalpy (ΔH) and entropy of activation (ΔS) at 98?°C were 42.9?kJ mol^?1, 74?kJ mol^?1, 39.9?kJ mol^?1 and ?92.3 J mol^?1 K^?1, respectively, for soluble starch hydrolysis. While ΔG of substrate binding (ΔG_E-S) and ΔG of transition state binding (ΔG_E-T) were 3.38 and ?14.1?kJ mol^?1, respectively. Whereas, EaD, Gibbs free energy (ΔG*), increase in the enthalpy (ΔH*) and activation entropy (ΔS*) for activation of the unfolding of transition state were 108, 107, 105?kJ mol^?1 and ?4.1 J mol^?1 K^?1. The thermodynamics of irreversible thermal inactivation of Tp-AmyS revealed that at high temperature the process involves the aggregation of the protein.     

Description of a new species of Anuretes (Copepoda: Caligidae) from Kerala

A new species ofAnuretes collected from the gills ofDiagramma crassispinum Day at Cape Comorin, India, is described in detail. The carapace of the three females obtained was folded ventrally likeHermilius on the gill filaments.     

Description of a new species of Lepeophtheirus (copepoda: caligidae) from Kerala

A new species of Lepeophtheirus collected from Plotosus anguillaris (Bloch) by the author is described in detail. All the related species of the genus are compared with Lepeophtheirus anguilli sp. nov.     

The E3 ubiquitin ligase Cul4b promotes CD4+ T cell expansion by aiding the repair of damaged DNA

The capacity for T cells to become activated and clonally expand during pathogen invasion is pivotal for protective immunity. Our understanding of how T cell receptor (TCR) signaling prepares cells for this rapid expansion remains limited. Here we provide evidence that the E3 ubiquitin ligase Cullin-4b (Cul4b) regulates this process. The abundance of total and neddylated Cul4b increased following TCR stimulation. Disruption of Cul4b resulted in impaired proliferation and survival of activated T cells. Additionally, Cul4b-deficient CD4⁺ T cells accumulated DNA damage. In T cells, Cul4b preferentially associated with the substrate receptor DCAF1, and Cul4b and DCAF1 were found to interact with proteins that promote the sensing or repair of damaged DNA. While Cul4b-deficient CD4⁺ T cells showed evidence of DNA damage sensing, downstream phosphorylation of SMC1A did not occur. These findings reveal an essential role for Cul4b in promoting the repair of damaged DNA to allow survival and expansion of activated T cells.

How does T cell receptor signaling prepare T cells for their rapid clonal expansion during pathogen invasion? This study shows that levels of the E3 ubiquitin ligase Cul4b increase following T cell activation; once expressed, Cul4b helps to maintain DNA integrity in CD4+ T lymphocytes by aiding in the repair of replication-induced DNA damage.     

Distribution of natural radionuclide40K in biotic and abiotic components of the Cauvery river system,Tiruchirapalli, India

Abiotic components like water and sediment, and biotic components such as mussels, fish and grass collected from Cauvery river at Tiruchirapalli were analysed for⁴⁰K activity. The highest level of⁴⁰K activity was found in the sediment (342 mBq g^-1 dry weight) and the lowest activity was found in water (2·209 mBq ml⁻¹). In the freshwater musselParreysia favidens (Benson)⁴⁰K activity was estimated in the total soft tissues and shells of mussels belonging to three different size groups. In all the size groups⁴⁰K activity was two times higher in shells (68–39 mBq g^-1 fresh weight) than in the total soft tissues (25–17 mBq g^-1 fresh weight). The results indicate that the younger mussels accumulated more⁴⁰K than the older ones. The ability of internal organs of mussels belonging to group III to accumulate⁴⁰K was in the following order: gills > digestive gland > foot > mantle. The values ranged from 47 to 18 mBq g⁻¹ fresh weight in the various organs. Concentration of⁴⁰K in the mussel was distinctly higher than in the grassEchinochloa colonum (J Koenig) (95 mBq g⁻¹ fresh weight), and the concentration of⁴⁰K in the bone of the fishCirrhina cirrhosa (Bloch) (126 mBq g⁻¹ fresh weight) was higher than to that of muscle (113 mBq g⁻¹ fresh weight)     

Pharmacodynamic studies on Polypodium vulgare (Linn.)

Aqueous extract of the root of P. vulgare (PV) produced CNS depressant effect. It decreased the spontaneous motor activity, prolonged the pentobarbitone induced hypnosis, reduced body temperature and increased the reaction time to pain stimuli. PV also caused prevention against supramaximal electroshock and pentylenetetrazol induced seizures. PV showed a positive inotropic and chronotropic effect on perfused frog heart and caused hypotension and tachycardia in anaesthetised dogs. The effects were blocked by propranolol. PV produced dose dependent inhibition of contractions of rabbit small intestine and the effect was blocked by propranolol. PV appears to possess CNS depressant and beta-adrenoceptor agonistic activities.