Structural and kinetic studies on ligand binding in wild-type and active-site mutants of penicillin acylase

Penicillin acylase catalyses the condensation of Calpha-substituted phenylacetic acids with beta-lactam nucleophiles, producing semi-synthetic beta-lactam antibiotics. For efficient synthesis a low affinity for phenylacetic acid and a high affinity for Calpha-substituted phenylacetic acid derivatives is desirable. We made three active site mutants, alphaF146Y, betaF24A and alphaF146Y/betaF24A, which all had a 2- to 10-fold higher affinity for Calpha-substituted compounds than wild-type enzyme. In addition, betaF24A had a 20-fold reduced affinity for phenylacetic acid. The molecular basis of the improved properties was investigated by X-ray crystallography. These studies showed that the higher affinity of alphaF146Y for (R)-alpha-methylphenylacetic acid can be explained by van der Waals interactions between alphaY146:OH and the Calpha-substituent. The betaF24A mutation causes an opening of the phenylacetic acid binding site. Only (R)-alpha-methylphenylacetic acid, but not phenylacetic acid, induces a conformation with the ligand tightly bound, explaining the weak binding of phenylacetic acid. A comparison of the betaF24A structure with other open conformations of penicillin acylase showed that betaF24 has a fixed position, whereas alphaF146 acts as a flexible lid on the binding site and reorients its position to achieve optimal substrate binding.     

Experimental investigation of the self- and N(2)-broadened continuum within the ν(2) band of water vapor

We present an experimental study of the self- and N(2)-broadened H(2) O continuum in microwindows within the ν(2) fundamental centered at ~1600 cm(-1). The continuum is derived from transmission spectra recorded at room temperature with a BOMEM Fourier transform spectrometer at a resolution of ~0.040 cm(-1). Although we find general agreement with previous studies, our results suggest that there is significant near-wing super-Lorentzian behavior that produces a highly wave-number-dependent structure in the continuum as it is currently defined.     

The history and development of the helium ion microscope

The helium ion microscope has recently emerged as a commercially available instrument. However, its roots go back more than 60 years to the development of the field ion microscope in Berlin, first reported in 1951. Over the intervening years, numerous researchers have pursued the development of a gas field ionization source with the goal of producing a suitable source for an ion microscope. This proved to be an elusive goal until early in this century when a number of discoveries led to a successful source, and shortly thereafter, an instrument fully able to exploit its advantages. Many individuals and many technical advances have come together to make this new class of microscope. The long history of this quest is reviewed along with the recent advances that led to the achievement of this milestone. A brief summary of the current status of the technology and its applications are given.     

Incidence of adenoviruses in raw and treated water

Adenoviruses are of major public health importance and are associated with a variety of clinical manifestations, i.e. gastroenteritis, eye infections and respiratory infections. The importance of water in the epidemiology of adenoviruses and the potential health risks constituted by adenoviruses in water sources and supplies are widely recognised. This study was conducted to assess the incidence of human adenoviruses in raw and treated water systems. Various raw and treated water were routinely monitored for the presence of adenoviruses, over a 1-year period (July 2000-June 2001). The supplies were derived from acceptable quality surface water sources using treatment processes, which conform to international standards for the production of safe drinking water. Adenoviruses were detected by firstly amplifying the viruses in cell cultures and then amplifying the extracted nucleic acids of these viruses using molecular techniques (nested PCR). The results indicated human adenoviruses present in 13 (12.75%) of the raw and 9 (4.41%) of the treated water samples tested. The combination of cell culture and nested PCR has proved to be a quick and reliable method for the detection of adenoviruses in water environments.     

应用Agent实现无线网络环境中的P2P

阐述了将传统的P2P服务扩展到无线网络环境的重要性、可行性、和面临的主要困难。在分析了一种系统架构MobiShare的基础上，提出了一种新的应用Agent技术实现P2P服务扩展的系统架构。该系统应用CAS对区域内的移动终端设备提供的服务进行管理；应用多Agent技术实现对环境信息的实时检测以实时更新服务的描述；应用移动Agent迁移技术实现对服务的发现和收集；异构Agent之间通信的描述则采用FIPA ACL语言。最后通过模拟实验说明了应用该系统架构所具有的优越性