Multiple solution conformations of the integrin-binding cyclic pentapeptide cyclo(-Ser-D-Leu-Asp-Val-Pro-). Analysis of the (phi, psi) space available to cyclic pentapeptides

The aqueous solution structure of the cyclic pentapeptide cyclo(-Ser-D-Leu-Asp-Val-Pro-) has been determined by two-dimensional 1H-NMR spectroscopy, combined with a conformational search and distance-geometry calculations. As many as five conformers in slow exchange were observed, and the rate of interconversion between components was measured from the build-up rates of exchange peaks. NMR data allowed the structures of the two predominant conformers to be determined. The major component (66%) contained a cis-proline as part of a type-VIa2 beta-turn encompassing residues Asp-Val-cis-Pro-Ser. The second component (16%) contained only trans-amide bonds, and a type-VIII beta-turn formed by residues Val-Pro-Ser-D-Leu. These structures are discussed in relation to the (phi, psi), space available to the cyclic pentapeptide, determined by a conformational search, and in relation to previously published cyclic-pentapeptide structures. The molecule exhibits activity in a scintillation-proximity assay for the inhibition of the interaction between the integrin very-late antigen-4 (VLA-4; alpha 4 beta 1) and vascular-cell-adhesion molecule-1 (VCAM-1). The structure/activity relationship of the LDV sequence is discussed and related to the recently published X-ray structure of VCAM-1. The relevance of the work to the design of anti-inflammatory drugs is discussed.     

Purification and characterization of a NADP+/NADPH-specific flavoprotein that is overexpressed in FdI- strains of Azotobacter vinelandii

Earlier studies have established that mutant strains of Azotobacter vinelandii that do not synthesize ferredoxin I (AvFdI) overexpress another protein designated Protein X (Morgan, T. V., Lundell, P. J., and Burgess, B. K. (1988) J. Biol. Chem. 263, 1370-1375). This protein has now been purified using two-dimensional gel electrophoresis as an assay. The purified protein is a monomer with M(r) approximately 29,000 which degrades slowly to a specific M(r) approximately 22,000 form when stored in solution. The native protein is bright yellow and contains noncovalently attached FAD that is reduced by either dithionite or NADPH without formation of a stable semiquinone. Titration with NADP+/NADPH gives an E0' value of approximately -327 mV versus SHE. Because this E0' is so close to that of the NADP+/NADPH couple it is not clear if Protein X is an NADPH oxidase or an NADP+ reductase in vivo. Comparison of the NH2-terminal sequence and other properties of Protein X with those of other proteins, suggests that it is likely to be related to the Escherichia coli ferredoxin NADP+ reductase (the fpr gene product), and affinity chromatography shows that Protein X binds specifically to AvFdI.     

电力市场环境下的稳定、安全与控制

电力市场化是全球电力工业都在热烈讨论和积极探索的热点课题 ,在中国电力市场化改革的今天 ,尤其具有重要的理论和实践意义。 2 0 0 2年 5月 1 3日至 1 8日 ,由清华港大深圳电力系统研究所主办的“电力市场新进展高级研讨会”在深圳清华大学研究院举行。在研讨会上 ,与会专家分别就电力市场研究和实践中的若干问题发表了演讲。本刊将主要内容摘录、汇编成文 ,奉献给大家 ,以便广大读者对电力市场的研究动态有比较全面的了解。在此 ,衷心感谢参加“电力市场新进展研讨会”的各位专家给予的大力支持和帮助 ,特别感谢香港大学 /浙江大学文福拴博士、香港大学严正博士在本文的摘编过程中提供的技术指导和具体帮助。