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We have investigated the in vitro metabolism of pectenotoxin-2 (PTX-2) using primary hepatocytes from Wistar rats in suspension. Purified PTX-2 was rapidly metabolized. Two major and several minor oxidized PTX-2 metabolites were formed, none of which had retention times corresponding to PTX-1, -11, or −13. Hydrolysis products, such as PTX-2 seco acid, were not observed. Preliminary multi-stage LC-MS analyses indicated that the major hepatic PTX-2 metabolites resulted from the insertion of an oxygen atom at the positions C-19 to C-24, or at C-44. The rapid oxidative metabolism may explain the low oral toxicity of PTXs observed in vivo studies., Highlights • PTX-2 is rapidly metabolized in rat hepatocytes. • Two major and several minor oxidized PTX-2 metabolites were formed. • The results may explain the low oral toxicity of PTXs observed in vivo studies.

Three laccases, a natural form and two recombinant forms obtained from two different expression hosts, were characterized and compared for paper pulp bleaching. Laccase from Pycnoporus cinnabarinus, a well known lignolytic fungus, was selected as a reference for this study. The corresponding recombinant laccases were produced in Aspergillus oryzae and A. niger hosts using the lacI gene from P. cinnabarinus to develop a production process without using the expensive laccase inducers required by the native source. In flasks, production of recombinant enzymes by Aspergilli strains gave yields close to 80 mg l -1. Each protein was purified to homogeneity and characterized, demonstrating that the three hosts produced proteins with similar physico-chemical properties, including electron paramagnetic resonance spectra and N-terminal sequences. However, the recombinant laccases have higher Michaelian (Km) constants, suggesting a decrease in substrate/enzyme affinity in comparison with the natural enzyme. Moreover, the natural laccase exhibited a higher redox potential (around 810 mV), compared with A. niger (760 mV) and A. oryzae (735 mV). Treatment of wheat straw Kraft pulp using laccases expressed in P. cinnabarinus or A. niger with 1-hydroxybenzotriazole as redox mediator achieved a delignification close to 75%, whereas the recombinant laccase from A. oryzae was not able to delignify pulp. These results were confirmed by thioacidolysis. Kinetic and redox potential data and pulp bleaching results were consistent, suggesting that the three enzymes are different and each fungal strain introduces differences during protein processing (folding and/or glycosylation).

This paper presents a biologically inspired, hardware-realisable spiking neuron model, which we call the Temporal Noisy-Leaky Integrator (TNLI). The dynamic applications of the model as well as its applications in Computational Neuroscience are demonstrated and a learning algorithm based on postsynaptic delays is proposed. The TNLI incorporates temporal dynamics at the neuron level by modelling both the temporal summation of dendritic postsynaptic currents which have controlled delay and duration and the decay of the somatic potential due to its membrane leak. Moreover, the TNLI models the stochastic neurotransmitter release by real neuron synapses (with probabilistic RAMs at each input) and the firing times including the refractory period and action potential repolarisation. The temporal features of the TNLI make it suitable for use in dynamic time-dependent tasks like its application as a motion and velocity detector system presented in this paper. This is done by modelling the experimental velocity selectivity curve of the motion sensitive H1 neuron of the visual system of the fly. This application of the TNLI indicates its potential applications in artificial vision systems for robots. It is also demonstrated that Hebbian-based learning can be applied in the TNLI for postsynaptic delay training based on coincidence detection, in such a way that an arbitrary temporal pattern can be detected and recognised. The paper also demonstrates that the TNLI can be used to control the firing variability through inhibition with 80% inhibition to concurrent excitation, firing at high rates is nearly consistent with a Poisson-type firing variability observed in cortical neurons. It is also shown with the TNLI, that the gain of the neuron (slope of its transfer function) can be controlled by the balance between inhibition and excitation, the gain being a decreasing function of the proportion of inhibitory inputs. Finally, in the case of perfect balance between inhibition and excitation, i.e. where the average input current is zero, the neuron can still fire as a result of membrane potential fluctuations. The firing rate is then determined by the average input firing rate. Overall this work illustrates how a hardware-realisable neuron model can capitalise on the unique computational capabilities of biological neurons. © 2002 Elsevier Science Ltd. All rights reserved. 15 7 891 908 Cited By :27

International audience; Three laccases, a natural form and two recombinant forms obtained from two different expression hosts, were characterized and compared for paper pulp bleaching. Laccase from Pycnoporus cinnabarinus, a well known lignolytic fungus, was selected as a reference for this study. The corresponding recombinant laccases were produced in Aspergillus oryzae and A. niger hosts using the lacI gene from P. cinnabarinus to develop a production process without using the expensive laccase inducers required by the native source. In flasks, production of recombinant enzymes by Aspergilli strains gave yields close to 80 mg l–1. Each protein was purified to homogeneity and characterized, demonstrating that the three hosts produced proteins with similar physico-chemical properties, including electron paramagnetic resonance spectra and N-terminal sequences. However, the recombinant laccases have higher Michaelian (K m) constants, suggesting a decrease in substrate/enzyme affinity in comparison with the natural enzyme. Moreover, the natural laccase exhibited a higher redox potential (around 810 mV), compared with A. niger (760 mV) and A. oryzae (735 mV). Treatment of wheat straw Kraft pulp using laccases expressed in P. cinnabarinus or A. niger with 1-hydroxybenzotriazole as redox mediator achieved a delignification close to 75%, whereas the recombinant laccase from A. oryzae was not able to delignify pulp. These results were confirmed by thioacidolysis. Kinetic and redox potential data and pulp bleaching results were consistent, suggesting that the three enzymes are different and each fungal strain introduces differences during protein processing (folding and/or glycosylation).

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An experimental study was carried out to establish whether the draft EEC method for the determination of the global migration of constituents from plastics packaging materials into fatty food stimulants could be applied to all plastics, including lacquers and laminates. Some difficulties were encountered in the use of the EEC method for melamine, for hotmelt-coated packaging materials and for laminates containing one or more layers of materials sensitive to moisture, such as paper, cardboard or regenerated cellulose film. Chemicals/CAS: cellulose, 61991-22-8, 68073-05-2, 9004-34-6; melamine, 108-78-1, 25778-04-5; Dietary Fats; Plastics

An experimental study was carried out to establish whether the draft EEC method for the determination of the global migration of constituents from plastics packaging materials into fatty food stimulants could be applied to all plastics, including lacquers and laminates. Some difficulties were encountered in the use of the EEC method for melamine, for hotmelt-coated packaging materials and for laminates containing one or more layers of materials sensitive to moisture, such as paper, cardboard or regenerated cellulose film. Chemicals/CAS: cellulose, 61991-22-8, 68073-05-2, 9004-34-6; melamine, 108-78-1, 25778-04-5; Dietary Fats; Plastics