Processing of Escherichia coli alkaline phosphatase: role of the primary structure of the signal peptide cleavage region

A wide range (69) of mutant Escherichia coli alkaline phosphatases with single amino acid substitutions at positions from -5 to +1 of the signal peptide were obtained for studying protein processing as a function of the primary structure of the cleavage region. Amber suppressor mutagenesis, used to create mutant proteins, included: (i) introduction of amber mutations into respective positions of the phoA gene; and (ii) expression of each mutant phoA allele in E. coli strains producing amber suppressor tRNAs specific to Ala, Cys, Gln, Glu, Gly, His, Leu, Lys, Phe, Pro, Ser and Tyr. Most amino acid substitutions at positions -3 and -1 resulted in a complete block of protein processing. These data give new experimental support for the "-3, -1 rule". Only Ala, Gly and Ser at position -1 allowed protein processing, and Ala provided the highest rate of processing. The results revealed the more conservative nature of the amino acids at the -1 position of signal peptides of Gram-negative bacteria as compared with those of eukaryotic organisms. Position -3 was less regular, since not only Ala, Ser and Gly, but also Leu and Cys at this position, allowed the processing. Mutations at position -4 had an insignificant effect on the processing. Surprisingly, efficient processing was provided mainly by large amino acid residues at position -2 and by middle-sized residues at position -5, indicating that the processing rate is affected by the size of amino acid residues not only at positions -1 and -3. Conformation analysis of the cleavage site taken together with the mutation and statistical data suggests an extended beta-conformation of the -5 to -1 region in the signal peptidase binding pocket.     

The protective reaction of the myocardium to ischemic damage

The morphological and functional consequences of epinephrine-induced myocardial infarction were studied in normo- (Wistar) and hypertensive (ISIAH) rats. After experimental myocardial infarction there was an irreversible transition to the "worn-out" stage or "plastic damage" to the myocardium. Thus, myocardial hibernation in ISIAH rats anticipates and determines the development of myocardial stunning, i.e., irreversible myocardial damage, whereas in the normotensive animals, the protective effect of hibernation is fully shown. The ontogenetic features of myocardial response of ISIAH rats to hypoxia promote transformation of adaptive hibernation and stunning to maladaptive pathological changes causing hypoxic alterations.     

Barnase mutant Ser57Ala: preparation and properties

Barnase, an extracellular ribonuclease produced by Bacillus amyloliquefaciens, belongs to a family of small microbial ribonucleases with similar structure and properties. These enzymes hydrolyze phosphodiester bonds on the 3' side of guanosine nucleotides in RNA. The guanylic specificity of barnase is more pronounced in the hydrolysis of dinucleotides or cyclonucleotide phosphates as substrates than in the hydrolysis of RNA or polynucleotides. To have an insight into the molecular basis of this phenomenon, we mutated amino acid residue Ser-57 in the "base recognition loop" of RNase Ba. The mutant protein was expressed in Escherichia coli producing system and purified for the study of the kinetic properties in the cleavage polynucleotide reactions. It was shown that the mutation of amino acid residue Ser-57 for Ala in the "recognition loop" of RNase Ba does not significantly influence the kinetic parametres of hydrolysis of polynucleotide substrates.     

樟洋燃机电厂电气主接线选择的考虑

结合燃机电厂的特点，介绍了樟洋燃机电厂电气主接线。说明了燃机电厂电气主接线选择时的原则，并根据樟洋燃机电厂的实例，阐述了是否装设发电机出口断路器等主接线选择时考虑到的一些问题。     

S7-200在炼钢上料主令控制器的应用

介绍了临钢炼钢厂上料系统主令控制器的构成、工作原理、软件编程以及设备性能等特点。     

火灾事故后喷射钢纤维混凝土在结构加固中的应用

在主配电室火灾烧伤事故处理中，结构钢筋较密，加固层较薄，采用喷射钢纤维混凝土加固修复，具有施工简便，快速，质量可靠，费用较低等优点，比一般圈套加固方法，工期可缩短二倍，节省修复费用50％左右，技术经济效果显。     

应用插管法消除砖煤气道窜漏

通过对太钢集团公司临钢焦化厂1号、2号焦炉砖煤气道窜漏的状况、窜漏的原因，进行检查、分析、研究，采用底部插管法消除砖煤气道窜漏，取得了很好的效果。为焦炉的正常生产、节能降耗以及延长焦炉寿命起到一定的作用。     

Fractal landscapes and molecular evolution: modeling the myosin heavy chain gene family

Mapping nucleotide sequences onto a "DNA walk" produces a novel representation of DNA that can then be studied quantitatively using techniques derived from fractal landscape analysis. We used this method to analyze 11 complete genomic and cDNA myosin heavy chain (MHC) sequences belonging to 8 different species. Our analysis suggests an increase in fractal complexity for MHC genes with evolution with vertebrate > invertebrate > yeast. The increase in complexity is measured by the presence of long-range power-law correlations, which are quantified by the scaling exponent alpha. We develop a simple iterative model, based on known properties of polymeric sequences, that generates long-range nucleotide correlations from an initially noncorrelated coding region. This new model-as well as the DNA walk analysis-both support the intron-late theory of gene evolution.     

Evidence on the corrosion-induced hydrogen embrittlement of the 2024 aluminium alloy

The present work aims to provide evidence of corrosion‐induced hydrogen embrittlement of the aircraft aluminium alloy 2024. An extensive experimental investigation involving metallographic and fractographic analyses as well as mechanical testing was performed. The corrosion exposure led to a moderate reduction in yield and ultimate tensile stress and a dramatic reduction in tensile ductility. Metallographic investigation of the specimens revealed a hydrogen‐rich embrittled zone just below the corrosion layer. Furthermore, fractographic analyses showed an intergranular fracture at the specimen surface followed by a zone of quasi‐cleavage fracture and further below an entirely ductile fracture. Mechanical removal of the corroded layers restored the yield and ultimate stress almost to their initial values but not the tensile ductility. The tensile ductility was restored to the level of the uncorroded material only after heat treatment at 495°C. Measurement of hydrogen evolution with temperature showed that by heating the corroded alloy at 495°C, the trapped hydrogen is released.