A comparative study of microwave and barrier discharge plasma for the regeneration of spent zeolite catalysts

Due to their acid characteristics and pore structure, which can induce high product selectivity; zeolite catalysts are used extensively in industry to catalyse reactions involving hydrocarbons. However, these catalysts can suffer from deactivation due to cracking reactions that result in the deposition of carbon leading to poisoning of the acid sites and blocking of the pores [1]. Depending upon the reaction and the particular catalyst involved this deactivation may take place over several months or even years but in some cases occurs in minutes. Therefore, zeolite catalysts are frequently reactivated / regenerated. This generally involves a thermal treatment involving air which results in oxidation of the carbon [2]. However, the oxidation of carbon is highly exothermic, and if not carefully controlled, results in the generation of exceedingly high localized temperatures which can destroy the zeolite structure and result in subsequent loss of catalyst activity. More conservative thermal treatments can result in incomplete regeneration and again a catalyst displaying inferior activity. This paper explores the use of non-thermal plasma which had been either generated using microwaves or via a barrier discharge to regenerate spent zeolite catalysts. The catalyst, H-mordenite, was tested for the disproportionation of toluene (Figure 1) using conventional heating. The spent catalyst was then regenerated using a plasma or conventional thermal treatment before having its activity re-evaluated for the toluene disproportionation reaction as previous. Fig. 1. Reaction Scheme for Toluene Disproportionation. Interestingly, not only is plasma regeneration highly effective but also catalysts can be regenerated in greatly reduced times. There is an additional advantage in that plasma regeneration can impart physical properties that result in a zeolite that is resistant to further deactivation. However, the results are highly dependent upon the experimental conditions involved for plasma regeneration. References Wu J, Leu L., Appl. Catal., 1983; 7:283-294. M. Guisnet and P. Magnoux, Deactivation of Zeolites by Coking. Prevention of Deactivation and Regeneration. In: Zeolite Microporous Solids: Synthesis, Structure, and Reactivity. E.G. Derouane, F Lemos, C. Naccache, F. Ramôa Ribeiro, Eds. Pages 437-456. Springer 1992

A novel secreted metzincin metalloproteinase from Bacillus intermedius

The mprBi gene from Bacillus intermedius 3-19 encoding a novel secreted metalloproteinase was identified. The mpriBi gene was expressed in an extracellular proteinase-deficient Bacillus subtilis BG 2036 strain and the corresponding protein was characterized biochemically. The 19. kDa MprBi protein was purified to homogeneity and sequenced by mass spectroscopy and Edman degradation methods. Amino acid sequence analysis of MprBi identified an active site motif HEYGHNFGLPHD and a conserved structural component Met-turn, both of which are unique features of the metzincin clan. Furthermore, MprBi harbors a number of distinct sequence elements characteristic of proteinase domains in eukaryotic adamalysins. We conclude that MprBi and similar proteins from other Bacillus species form a novel group of metzincin metalloproteinases in prokaryotes. © 2010 Federation of European Biochemical Societies

Determination of three amino acids causing alteration of proteolytic activities of staphylococcal glutamyl endopeptidases.

Abstract Staphylococcus aureus, Staphylococcus epidermidis and Staphylococcus warneri secrete glutamyl endopeptidases, designated GluV8, GluSE and GluSW, respectively. The order of their protease activities was GluSE<GluSW<<GluV8. The present study investigated the mechanism that causes these differences. Expression of chimeric proteins between GluV8 and GluSE revealed that the difference was primarily attributed to amino acids at residues 170-195, which defined the intrinsic protease activity, and additionally to residues 119-169, which affected the proteolysis sensitivity. Among nine substitutions present in residues 170-195 of the three proteases, the substitutions at positions 185, 188 and 189 were responsible for the changes in their activities; and the combination of W185, V188 and P189, which naturally occurred on GluV8, exerted the highest protease activity. Among them, W185 and P189 were indispensable for the full activity; but V188 could be replaced by hydrophobic amino acids. These three amino acid residues appeared to create a substrate-binding pocket together with the catalytic triad and the N-terminal V1, and therefore, defined the K(m) values of the proteases. This study also describes the way to produce a chimeric form of GluSE and GluV8 that was resistant to proteolysis, and therefore, possessed activity 4-fold higher than that of the wild-type recombinant GluV8

Получение рекомбинантных нейротрофинов человека для биомедицинских исследований

The genes of nerve growth factor (NGF), brain neurotrophic factor (BDNF) and human neurotrophic factor 3 (NT-3) were cloned and expressed in Escherichia coli. Methods of purification and renaturation of the proneurotrophins were developed. It was shown that the recombinant pro-NGF, pro-BDNF and pro-NT-3 induce a differentiation of chicken dorsal root ganglia cell culture.Клонированы гены фактора роста нервов (NGF), нейротрофического фактора головного мозга (BDNF) и нейротрофического фактора 3 (NT-3) человека и осуществлена их экспрессия в клетках Escherichia coli. Разработаны схемы очистки и ренатурации соответствующих пробелков. Продемонстрировано, что рекомбинантные про-NGF, про-BDNF, про-NT-3 оказывают дифференцирующее действие на культуру спинномозговых ганглиев эмбрионов кур

The expression of the serine proteinase gene of Bacillus intermedius in Bacillus subtilis

The gene encoding for Bacillus intermedius serine proteinase was cloned and the complete nucleotide sequence was determined. Gene expression was explored in the protease-deficient strain Bacillus subtilis AJ73 during different stages of growth. Catabolite repression involved in control of proteinase expression during transition state and onset of sporulation was not efficient at the late stationary phase. Salt stress leads to induction of serine proteinase production during B. subtilis AJ73(pCS9) post-exponential growth. Expression of proteinase in B. subtilis deg-mutants may be controlled by DegU regulator. B. subtilis spo0-mutants failed to accomplish B. intermedius proteinase production. These data suggest complex network regulation of B. intermedius serine proteinase expression, including the action of spo0, degU, catabolite repression and demonstrate changes in control of enzyme biosynthesis at different stages of growth. © 2006 Elsevier GmbH. All rights reserved

Structural Basis for Specificity of Propeptide-Enzyme Interaction in Barley C1A Cysteine Peptidases

C1A cysteine peptidases are synthesized as inactive proenzymes. Activation takes place by proteolysis cleaving off the inhibitory propeptide. The inhibitory capacity of propeptides from barley cathepsin L and B-like peptidases towards commercial and barley cathepsins has been characterized. Differences in selectivity have been found for propeptides from L-cathepsins against their cognate and non cognate enzymes. Besides, the propeptide from barley cathepsin B was not able to inhibit bovine cathepsin B. Modelling of their three-dimensional structures suggests that most propeptide inhibitory properties can be explained from the interaction between the propeptide and the mature cathepsin structures. Their potential use as biotechnological tools is discussed

Glutamyl endopeptidases: The puzzle of substrate specificity

Glutamyl endopeptidases (GEPases) are chymotrypsin-like enzymes that preferentially cleave the peptide bonds of the α-carboxyl groups of glutamic acid. Despite the many years of research, the structural determinants underlying the strong substrate specificity of GEPases still remain unclear. In this review, data concerning the molecular mechanisms that determine the substrate preference of GEPases is generalized. In addition, the biological functions of and modern trends in the research into these enzymes are outlined. © 2017 Park-media, Ltd