Combustion of cotton gin residues in a lime kiln reactor

Combustion of cotton gin residues was studied in the furnace of a continuous-operation, modern lime kiln. During its first period of operation, the plant experienced some problems; corrosion of the refractory bricks, difficulty in controlling the temperature at the main burner, a hard mass of lime building up inside the kiln and around the main burner. However, in spite of the problems successful production of lime was finally achieved. Measurements show that the use of cotton gin residues as a combustible material does not create any significant changes either in the quality of the lime or in the environment.     

Flow-injection determination of streptomycin residues in milk using the luminol-periodate-Mn2+ chemiluminescence system.

A novel flow-injection method with chemiluminescence detection was developed for the determination of streptomycin residues in milk, based on the enhancement by streptomycin of the luminol-potassium periodate-Mn(2+) chemiluminescence system. The assay allowed analysis of streptomycin residues in whole milk samples ( approximately 3.5% fat) after sample work-up procedures. The limit of detection was 5.16 x 10(-9) mol/L for milk, and was far below the regulations of maximum residue limits (MRLs). The relative standard deviation (RSD) for 8.66 x 10(-8) mol/L streptomycin was 1.94% (n = 15) in milk. The results obtained for the assay of streptomycin residues in milk was comparable with those obtained by the official methods (ELISA) and demonstrated good accuracy and precision. The possible mechanism is briefly discussed.     

Catalytic Production of Liquid Fuels from Organic Residues of Rendering Plants

Anaerobic low temperature conversion (LTC) converts organic residues such as animal meal or meat and bone meal (MBM) to bio‐crude, a solid product, containing carbon and phosphorus, reaction water and non‐condensable gases. The yield of bio‐crude increases with the content of volatile solids. The efficiency of the conversion as well as the calorific value of the liquid fuel produced are favorably affected by the partial recycling of inorganic constituents, high amounts of volatile solids and a low percentage of heteroatoms present in the feeding material. Heating values are 32.3 MJ/kg for bio‐crude from animal meal and 19.5 MJ/kg for bio‐crude from MBM. Both bio‐crude and animal fat produced were effectively converted in a vertical reactor construction with a fixed bed of aluminosilicates of the zeolite family or acidic clays, respectively. Products are bio‐fuels of varying chemical qualities. Depending on the reaction temperature and the catalyst type, aliphatic hydrocarbons (T = 400 °C, ～97 %) or alkylbenzenes (T = 550 °C) are the main products. The calorific values of these bio‐fuels are in a range from 40.1 to 41.9 MJ/kg and the kinematic viscosities are between 0.9 and 2.29 mm²/s. The solid products of LTC from different biomass (sludge, animal meal, MBM) contain a significant amount of phosphorus. In the case of the solid product from MBM it was as high as 242 mg P₂O₅/g. Solubility in citric acid showed that in the case of MBM, 98.8 % of total phosphorus is potentially available to plants. Pot experiments demonstrated a similar plant growth as with other organic fertilizers.     

Designed β-sheet-forming peptide 33mers with potent human bactericidal/permeability increasing protein-like bactericidal and endotoxin neutralizing activities

Novel peptide 33mers have been designed by incorporating β-conformation stabilizing residues from the β-sheet domains of α-chemokines and functionally important residues from the β-sheet domain of human neutrophil bactericidal protein (B/PI). B/PI is known for its ability to kill bacteria and to neutralize the action of bacterial endotoxin (lipopolysaccharide, LPS) which can induce septic shock leading to eventual death. Here, the goal was to make short linear peptides which demonstrate good β-sheet folding and maintain bioactivity as in native B/PI. A library of 24 peptide 33mers (βpep-1 to βpep-24) were synthesized with various amino acid substitutions. CD and NMR data acquired in aqueous solution indicate that βpep peptides form β-sheet structure to varying degrees and self-associate as dimers and tetramers like the α-chemokines. Bactericidal activity toward Gram-negative Pseudomonas aeruginosa was tested, and βpep-19 was found to be only about 5-fold less potent (62% kill at 1.2×10^?7 M) than native B/PI (80% kill at 2.9×10^?8 M). At LPS neutralization, βpep-2 and -23 were found to be most active (66–78% effective at 1.2×10^?6 M), being only about 50–100-fold less active than B/PI (50% at 1.5×10^?8 M). In terms of structure–activity relations, β-sheet structural stability correlates with the capacity to neutralize LPS, but not with bactericidal activity. Although a net positive charge is necessary for activity, it is not sufficient for optimal activity. Hydrophobic residues tend to influence activities indirectly by affecting structural stability. Furthermore, results show that sequentially and spatially related residues from the β-sheet domain of native B/PI can be designed into short linear peptides which show good β-sheet folding and retain much of the native activity. This research contributes to the development of solutions to the problem of multiple drug-resistant, opportunistic microorganisms like P. aeruginosa and of agents effective at neutralizing bacterial endotoxin.     

Design, synthesis and catalytic activity of a serine protease synthetic model

Summary The design, synthesis and catalytic properties of a cyclic branched peptide carrier that possesses the catalytic triad residues of the serine proteases is reported. The synthesis of the peptide model was totally completed on solid support using three different orthogonal amino protecting groups. Hydrolytic activity measurements against Suc-Ala-Ala-Ala-pNA substrate showed that it is hydrolysed by the peptide model to a small extent. Despite this small hydrolytic activity, it is the first time, to our knowledge, that hydrolysis of such a substrate is reported by an enzyme model compound. Contrary, this enzyme model peptide showed considerable activity against the Boc-Ala-pNP substrate (k _cat =0.414 min⁻¹ andK _m =0.228 mm). These results suggest that the designed carrier brings in appropriate contact the catalytic triad residues (Ser, His, Asp) resulting in the obtained hydrolytic activity.     

Formation of isoaspartate 99 in bovine and porcine somatotropins

Asparagine 99 in bovine (BST) and porcine somatotropins (PST) was converted to an isoaspartate residue during incubation at neutral or alkalinepH. Isoaspartate 99 BST or isoaspartate 99 PST was resolved from the normal somatotropin by reversed-phase high-performance liquid chromatography (HPLC). The altered peptide of residues 96–108 which contains isoaspartate 99 was detected by tryptic peptide mapping of the modified BST or PST. Amino acid sequencing, amino acid analysis, mass spectrometry, and co-elution with a chemically synthesized peptide containing isoaspartate 99 were used to demonstrate the existence of isoaspartate in the modified peptides. Peptide bond cleavage between Asn 99 and Ser 100 also occurred during incubation of BST and PST at neutral or alkalinepH. This chemically cleaved product was resolved on reversed-phase HPLC from both the isoaspartate 99 and normal somatotropin molecules.     

基于弹性网络模型的蛋白质变构路径与关键残基识别研究

目的 变构效应在蛋白质生物学功能执行过程中发挥着重要的调控作用，如何基于蛋白质空间结构，有效识别变构信号的传播路径和关键的残基位点是蛋白质结构-功能关系研究领域的热点科学问题。方法 本研究利用基于弹性网络模型（elastic network model，ENM）的力分布计算方法，通过分析蛋白质对外力的响应过程，来识别体系的变构路径以及变构过程中的关键残基。在该方法中，对蛋白质的关键变构位点施加外力，通过对体系形变以及内力分布情况的分析，有效识别与外力承载区域形变相耦合的关键残基，从而得到力信号在蛋白质结构内的传播路径。结果 利用该方法研究了人类磷酸甘油酸激酶（human phosphoglycerate kinase，hPGK）和蛋白质酪氨酸磷酸酶（protein tyrosine phosphatase，PTP）PDZ2结构域的变构调控路径和关键残基。对于hPGK，识别出从底物结合位点到铰链区的两条变构信号传导路径。对于PTP PDZ2，也成功识别出从配体结合位点传递到蛋白质远端的两条长程变构调控路径。计算结果与实验和分子动力学（molecular dynamics，MD）模拟得到的结果一致。结论 本研究为蛋白质体系关键残基识别及变构路径研究提供了有效的分析方法。