CALL混杂复合材料的弯曲试验研究

用云纹干涉法，研究了单向增强CALL混杂复合材料在纤维方向和垂直于纤维方向的弯曲特征。

An experimental-study of the bending behavior of call hybrid composites

The bending behavior and damage characteristics of CALL (Carbon fiber/epoxy/AL Laminate) hybrid composites have been studied by moire interferometry. The shear strain distribution along the cross-section and the forms of damage of bending beams are obtained. The results show that the magnitude of the shear strain in a carbon/epoxy layer is obviously larger than that in a corresponding aluminum layer and the shear strain distribution of a CFRP layer along the cross-section conforms basically to a parabolic distribution curve, as for the shear strain distribution in aluminum layers along the cross-section. Shear damage, either in the interfaces or in carbon-fiber/epoxy laminae, and tensile failure of CFRP laminae in the tension surface represent, respectively, the damage forms of the longitudinal and transverse bending specimen.

Trimeresurus stejnegeri snake venom plasminogen activator - Site-directed mutagenesis and molecular modeling

The specific plasminogen activator from Trimeresurus stejnegeri venom (TSV-PA) is a serine proteinase presenting 23% sequence identity with the proteinase domain of tissue type plasminogen activator, and 63% with batroxobin, a fibrinogen clotting enzyme from Bothrops atrox venom that does not activate plasminogen. TSV-PA contains six disulfide bonds and has been successfully overexpressed in Escherichia coli (Zhang, Y., Wisner, A., Xiong, Y. L,, and Bon, C, (1995) J. Biol. Chem. 270, 10246-10255), To identify the functional domains of TSV-PA, we focused on three short peptide fragments of TSV-PA showing important sequence differences with batroxobin and other venom serine proteinases. Molecular modeling shows that these sequences are located in surface loop regions, one of which is next to the catalytic site, When these sequences were replaced in TSV-PA by the equivalent batroxobin residues none generated either fibrinogen-clotting or direct fibrinogenolytic activity, Two of the replacements had little effect in general and are not critical to the specificity of TSV-PA for plasminogen. Nevertheless, the third replacement, produced by the conversion of the sequence DDE 96a-98 to NVI, significantly increased the K-m for some tripeptide chromogenic substrates and resulted in undetectable plasminogen activation, indicating the key role that the sequence plays in substrate recognition by the enzyme.

Molecular dynamics simulation on the complex of the tobramycin and 16S rRNA a site

A 3. 6 ns molecular dynamics simulation was carried out on the complex system of tobramycin and 16S rRNA in order to understand the speciality recognition mechanism between tobramycin and 16S rRNA at the molecular level. The results demonstrate that two l

Secondary structural analysis of the mRNA regions encoding the hemagglutinin cleavage site basic amino acids of the avian influenza virus H5N1 subtype samples

Here we report the codon bias and the mRNA secondary structural features of the hemagglutinin (HA) cleavage site basic amino acid regions of avian influenza virus H5N1 subtypes. We have developed a dynamic extended folding strategy to predict RNA secondar

Site-directed PEGylation of trichosanthin retained its anti-HIV activity with reduced potency in vitro

Trichosanthin (TCS) was the first ribosome inactivating protein found to possess anti-HIV-1 activity. Phase I/II clinical trial of this compound had been done. Antigenicity and short plasma half-life were the major side effects preventing further clinical trial. Modification of TCS is therefore necessary to revive the interest to develop this compound as an anti-HIV agent. Three potential antigenic sites (Ser-7, Lys-173, and Gln-219) were identified by computer modeling. Through site-directed mutagenesis, these three antigenic amino acids were mutated to a cysteine residue resulting in 3 TCS mutants, namely S7C, K173C, and Q219C. These mutants were further coupled to polyethylene glycol with a molecular size of 20 kDa (PEG) via the cysteine residue. This produced another three TCS derivatives, namely PEG(20)k-S7C, PEG(20)k-K173C, and PEG(20)k-Q219C. PEGylation had been widely used recently to decrease immunogenicity by masking the antigenic sites and prolong plasma half-life by expanding the molecular size. The in vitro anti-HIV-1 activity of these mutants and derivatives was tested. Results showed that the anti-HIV-1 activity of S7C, K173C, and Q219C was decreased by about 1.5- to 5.5-fold with slightly lower cytotoxicity. On the other hand, PEGylation produced larger decrease (20- to 30-fold) in anti-HIV activity. Cytotoxicity was, however, weakened only slightly by about 3-fold. The in vitro study showed that the anti-HIV activity of PEGylated TCS was retained with reduced potency. The in vivo activity is expected to have only slightly changed due to other beneficial effects like prolonged half-life. (C) 2004 Elsevier Inc. All rights reserved.