Spermine as a porcine pancreatic elastase activator: spectroscopic and molecular simulation studies

Abstract

The aim of this study was to investigate the spermine effect on the thermal denaturation, conformation and activity of elastase at three temperatures of 303, 313 and 323?K in the Tris buffer, at pH 8.5, using UV–vis spectrophotometry, spectrofluorometry and circular dichroism as well as molecular docking and molecular simulation. The increased absorption of elastase in the presence of spermine suggested a change in the environment of tryptophan. It was found that under the influence of spermine, the emission intensity of elastase extremely was reduced, and the use of the Stern-Volmer equation showed that some static quenching had occurred. The thermodynamic parameters values (enthalpy and entropy) and the molecular docking technique also revealed that van der Waals forces or hydrogen bonding interactions played an important role in the binding process. The spermine–elastase complex formation led to increasing the value of the catalytic constant (k_cat). So it could be considered as an activator. Slight changes were observed in the second structure of elastase (1.06% increase for the α-helix and 0.048% decrease the β-sheet) and the thermal stability effect. Molecular docking results also demonstrated that spermine could bind to porcine pancreatic elastase, and van der Waals forces or hydrogen bonding interactions played the major role in the binding process. Overall, our results showed that spermine could induce structural alterations in elastase, acting as a partial stabilizer and an activator for the enzyme.

Communicated by Ramaswamy H. Sarma     

Dual Atrioventricular Nodal Pathways Physiology: A Review of Relevant Anatomy,Electrophysiology, and Electrocardiographic Manifestations

More than half a century has passed since the concept of dual atrioventricular (AV) nodal pathways physiology was conceived. Dual AV nodal pathways have been shown to be responsible for many clinical arrhythmia syndromes, most notably AV nodal reentrant tachycardia. Although there has been a considerable amount of research on this topic, the subject of dual AV nodal pathways physiology remains heavily debated and discussed. Despite advances in understanding arrhythmia mechanisms and the widespread use of invasive electrophysiologic studies, there is still disagreement on the anatomy and physiology of the AV node that is the basis of discontinuous antegrade AV conduction. The purpose of this paper is to review the concept of dual AV nodal pathways physiology and its varied electrocardiographic manifestations.     

Improved microspore embryogenesis induction and plantlet regeneration using putrescine,cefotaxime and vancomycin in Brassica napus L.

The effects of three periods of exposure (12, 24 and 48 h) to different levels of putrescine (0, 0.2, 0.5, 1.0, 2.0 and 5.0 mg l^?1), as well as three incubation periods (24, 48 and 72 h) to different levels of cefotaxime and vancomycin (0, 50, 100, 200 and 500 mg l^?1) on microspore embryogenesis of rapeseed cv. ‘Hyola 401’ were assessed. Microspore embryogenesis was enhanced about threefold compared with untreated culture following 48 h treatment with 0.2 mg l^?1 putrescine. Putrescine treatment at 0.5 mg l^?1 for 48 h effectively induced root formation and increased normal plantlet regeneration by 92 % when microspore-derived embryos (MDEs) were transferred to regeneration medium. The highest embryo yield (184.2 embryos Petri dish^?1) was possible when induction medium was supplemented with 50 mg l^?1 cefotaxime for 24 h and the highest normal regeneration was observed in cultures exposed to 50 and 100 mg l^?1 at all durations tested. More abnormal MDEs (76 and 82 %) were observed when microspores treated with 200 and 500 mg l^?1 cefotaxime many of which failed to regenerate normally and resulted in callusing. Vancomycin at 100 mg l^?1 during the 48 h exposure increased the number of MDEs (181.6 embryos Petri dish^?1) in contrast to untreated cultures (93.6 embryos Petri dish^?1) but, normal plantlet regeneration decreased as vancomycin level increased and high callusing (84 and 90 %) was observed with 200 and 500 mg l^?1 for 72 h. Microspore embryogenesis and plant regeneration could be improved by putrescine, cefotaxime and vancomycin when appropriate levels and durations of incubation were selected.     

Enhanced Efficiency of In Vitro Rootstock Micro-propagation Using Silica-Based Nanoparticles and Plant Growth Regulators in Myrobalan 29C (Prunus cerasifera L.)

Different experiments were conducted to establish and optimize an efficient in vitro micropropagation protocol for Myrobalan 29C rootstocks. Disinfection of initial explants with AgNPs (2.5%) reduced the needed amount of NaClO (5.0%) by half. The highest rates of induced active buds were obtained in the DKW (90.63%), MS (86.67%), modified MS (82.22%), and WPM (78.15%) culture media supplemented with BAP (2.22 μmol L^?1)?+?GA₃ (2.88 μmol L^?1)?+?IBA (0.05 μmol L^?1)?+?Fe-EDDHA (228.72 μmol L^?1). The highest quality of the proliferated shoots (5.0) was also achieved using DKW medium. Inclusion of GA₃ (5.76 μmol L^?1), Fe-EDDHA (114.36–228.72 μmol L^?1), or BAP (2.22 μmol L^?1) were also able to enhance the rate of shoot multiplication. Compared to the agar-solidified culture system, the established shoots proliferated more efficiently when immersed by bioreactor in the liquid DKW culture medium on a regular basis. Exogenous application of silica-based nanoparticles (NPs) including the chemically synthesized silica NPs (TSiO₂ NPs, 1.0 ppm), rice husk derived biogenic silica NPs (RSiO₂ NPs, 10.0 ppm), or amine modified silica NPs (ASiO₂ NPs, 10.0 ppm) to the multiplication medium increased the number of regenerated lateral shoots by 520%, 360%, and 349%, respectively. Proliferated shoots with well-developed root system were obtained from the rooting medium supplemented with 19.68 μmol L^?1 IBA. Our results indicated that the rootstocks of Myrobalan 29C could be efficiently propagated under in vitro condition providing proper culture medium and optimal concentrations of additives and plant growth regulators were adopted.

     

On problem solving with Hopfield neural networks

Hopfield and Tank have shown that neural networks can be used to solve certain computationally hard problems, in particular they studied the Traveling Salesman Problem (TSP). Based on network simulation results they conclude that analog VLSI neural nets can be promising in solving these problems. Recently, Wilson and Pawley presented the results of their simulations which contradict the original results and cast doubts on the usefulness of neural nets. In this paper we give the results of our simulations that clarify some of the discrepancies. We also investigate the scaling of TSP solutions found by neural nets as the size of the problem increases. Further, we consider the neural net solution of the Clustering Problem, also a computationally hard problem, and discuss the types of problems that appear to be well suited for a neural net approach.