Characterization of the glycosyltransferase activity of desVII: analysis of and implications for the biosynthesis of macrolide antibiotics

In vitro catalytic activity of DesVII, the glycosyltransferase involved in the biosynthesis of methymycin, neomethymycin, narbomycin, and pikromycin in Streptomyces venezuelae, is described. This is the first report of demonstrated in vitro activity of a glycosyltransferase involved in the biosynthesis of macrolide antibiotics. DesVII is unique among glycosyltransferases in that it requires an additional protein component, DesVIII, as well as basic pH for its full activity.     

C[bond]H- - -O hydrogen bonds in beta-sheetlike networks: combined X-ray crystallography and high-pressure infrared study

Close interactions of the C(alpha)[bond]H- - -O type have been analyzed via X-ray crystallography and high-pressure infrared spectroscopy. The results demonstrate that the C(alpha)[bond]H- - -O interactions can offer an additional stability to the beta-sheet formation. X-ray structural data suggest that while 1-acetamido-3-(2-pyrimidinyl)-imidazolium bromide exhibits a bilayer stacking, the PF(6)(-) salt reveals a beta-sheetlike pattern. The appearance of the free-NH infrared absorption indicates that the conventional N[bond]H- - -O or N[bond]H- - -N hydrogen bonds do not fully dominate the packing for the PF(6)(-) salt. The high-pressure infrared study suggests that the C(alpha)[bond]H- - -O hydrogen bonds are the important determinants for the stability of the PF(6)(-) salt. This study also verifies that the imidazolium C[bond]H stretching frequency shifts to a longer wavelength upon the formation of the C[bond]H- - -O hydrogen bonds.     

Recombinant polyclonal antibody libraries

We describe a technology for generating recombinant polyclonal antibody libraries (PCALs) that enables the creation and perpetuation of standardized mixtures of polyclonal whole antibodies specific for a multiantigen (or polyantigen). Therefore, this technology combines the advantages of targeting multiple antigenic determinants -- high avidity, low likelihood of antigen 'escape variants', and efficient mediation of effector functions, with the advantages of using monoclonal antibodies -- unlimited supply of standardized reagents and the availability of the genetic material for desired manipulations. The technology for generating recombinant polyclonal antibody libraries begins with the creation of phage display Fab (antibody) libraries. This is followed by selection of sublibraries with desired antigen specificities, and mass transfer of the variable region gene pairs of the selected sublibraries to a mammalian expression vector for generation of libraries of polyclonal whole antibodies. We review here our experiments for selection of phage display antibody libraries against microbes and tumor cells, as well as the recent literature on the selection of phage display antibody libraries to multiantigen targets.     

活性钴引起α—溴代酮的反应

近年来,活性钛,活性镍等金属试剂正被用于有机合成并引起人们的关注。最近,对活性钴引起有机反应的研究也日益增多。例如在活性钴试剂作用下,卤代芳烃脱卤偶联得到联苯化合物,α,α—二氯二苯基甲烷脱卤得到四苯乙烯,富马酸与二溴甲烷可以发生不对称环丙烷化反应等。本文报道活性钴试剂引起α—溴代酮的反应。     

Electrokinetic flow through an elliptical microchannel: effects of aspect ratio and electrical boundary conditions

The electrokinetic flow of an electrolyte solution through an elliptical microchannel is studied theoretically. The system under consideration simulates the flow of a fluid, for example, in vein. We show that, for a constant cross-sectional area, both the electroosmotic volumetric flow rate and the streaming potential increase monotonically with an increase in the aspect ratio, and both the total electric current and the electroviscous effect may exhibit a local minimum as the aspect ratio varies. Also, for a constant average potential on the channel wall, the difference between the results based on three kinds of boundary conditions, which include constant surface charge, constant surface potential, and charge-regulated surface, is inappreciable if the hydraulic diameter is larger than 1 mum.     

A Convenient Halogenation Procedure for the Preparation of α-Halocarbonyl Compounds

Except for substituted acetophenones (p-Y-C₆H₄COCH₃, Y=H, Br, CH₃O), simple ketones, β-ketoesters and 1,3-diketones reacted smoothly with a preformed homogeneous mixture of hydrochloric acid and potassium permanganate in acetonitrile to give moderate to good yields of the corresponding α-chlorocarbonyl compounds. Mixtures of α-chloro- and α,α-dichlorocarbonyl compounds were obtained for substituted acetophenones. Brominations proceeded similarly with higher yields when the hydrochloric acid was replaced with hydrobromic acid.     

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Low-power high-efficiency wavelength conversion based on modulational instability in high-nonlinearity fiber

Bandwidth and peak efficiency are enhanced for wavelength conversion based on induced modulation instability by use of dispersion-shifted fiber in which the nonlinearity (n(2)/A(eff)) is enhanced by a factor of ~4.5 over that of conventional dispersion-shifted fiber. We experimentally obtain a peak conversion efficiency as high as 28 dB over a 40-nm bandwidth with 600 mW of peak pump power. Considerations for further enhancement of fiber-based wavelength conversion are also discussed.