Identification of Residue Involved in Nucleotidyltransferase Activity of LinA from Staphylococci by Site-directed Mutagenesis

The lincosamide class of antibacterials is widely used for the treatment of a broad spectrum of infections, and one prevalent route of resistance to lincosamides in pathogenic gram-positive cocco is antibiotic modification. Enzymes encoded by lin genes, belonging to nucleotidyltransferase superfamily, catalyze adenylylation to inactivate lincosamides. LinA can adenylylate lincosamides at either 3?-or 4?-OH of the methylthiolincosamide sugar. The crystal structure of LinA/lincomycin has confirmed its active site. However, the residue interacting with nucleotidyl donors remains elusive. Here, we modeled the complex structure of LinA/lincomycin/Mg~(2+)/AMPCPP to reveal a putative pocket for nucleotidyl donors and suggested the residue R45 in this pocket involved in the recognition of donor substrates NTP and catalysis. ITC and enzyme activity assays show that the mutation of residue R45 impairs LinA nucleotidyltransferase activity in vitro. This work provides insights into the molecular mechanism of the nucleotide binding and transferring activity of antibiotic NTases.     

GEOCHEMISTY OF BICYCLIC ALKANES IN SEDIMENTS, COAL AND CRUDE OILS

By using GC-MS to analyze the extracts of source rocks, coal and crude oil samplesformed in different sedimentary environments in China, New Zealand and Australia, twenty-two compounds of five types of bicyclic alkanes have been dis covered in the samples. Thispaper makes an exposition of stereochemical structure, abundance and distributive features ofthese compounds and their relation to sedimentary environments and thermal evolution. Furt-thermore, it demonstrates how the abundance ratios of bicyclic alkanes to steranes and ter-panes, drimane to homodramane and the relative abundance of C_(15),C_(16),C_(12)-C_(14) series of bicyclic-alkane compounds can be used to judge and determine types of oil and gas forming environ-ments (the depositive environments of source rocks from which the oil and gas wereformed), characteristics of source rocks and degree of maturation.     

中国陆相油气的形成和运移(Ⅱ)

本文(Ⅰ)着重研究了中国陆相湖盆沉积物中有机质向油气演化的过程.本文(Ⅱ)阐明了现代青海湖沉积物埋藏初期及早期成岩作用过程中有机质的演化特征.其结果表明陆相有机质大量开始向石油转化的深度随不同地区、不同时代、不同类型的有机质而异.最后,运用特征有机化合物、稀有气体同位素等资料,结合构造发展史阐述我国陆相油气运移的类型、规模和途径.指出近油源短距离是陆相油气运移的基本特征.     

超临界CO2在泥岩生物标志物分析中的应用与索氏抽提技术的实验对比

应用超临界萃取/气相色谱-质谱技术测定泥岩中的正构烷烃、藿烷,其有机地化参数与经典索氏抽提基本相符.该方法样品用量少,且高效、快速、无污染和危险,适用于有机地球化学研究中稀少地质样品生物标志化合物及一些分子标志物的分析检测工作.     

南极湖泊现代沉积物超临界流体萃取的气相色谱-质谱分析

近年来超临界流体萃取技术在海洋、湖泊、土壤及河流沉积物的生物地球化学研究领域应用日益广泛和深入，其中生物标记化合物的研究，不仅可以揭示有机质在沉积、成岩作用过程中的演化，而且还可为反映古环境和古气候状况提供重要信息。     

原油、煤和沉积物中二环烷烃的地球化学意义

用GC-MS技术分析了中国、新西兰和澳大利亚不同沉积环境形成的原油、岩石和煤样抽提物中的二环烷烃。这些样品普遍含有C_(12)—C_(13),二环烷烃和C_(14)—C_(16)二环倍半萜化合物,共检出22个谱峰。本文讨论了它们的构型、丰度和分布特征及其与沉积环境和热演化的相关性;根据二环烷烃和二环倍半萜烷烃与甾、萜烷的相对丰度、C_(12)—C_(14)与C_(15)和C_(16)之间的相对丰度以及DHR值(补身烷与高补身烷的比值)可判识油气成因类型、形成环境、母源特征及成熟作用的程度。     

中国陆相油气的形成和运移(Ⅰ)

本文总结了我国大量油田和地质、地球化学资料,从古气候、含盐量、沉积水动力、大地构造等各方面,论证了“陆相潮湿拗陷”是陆相油气形成的基本规律.指出:潮湿-半潮湿气候、地壳长期稳定下陷、淡水-微咸水介质、湖泊环流中心水动力平静区是油气形成比较有利的地带.并从中、新生代“陆相潮湿拗陷”的形成和发展,探讨了中国陆相油气田分布的一般规律.     

超临界流体萃取及GC-MS对极地现代沉积物的分析

应用超临界萃取/气相色谱-质谱技术测定南极现代沉积物中的正构烷烃、甾烷、藿烷,其分析结果与经典索氏抽提基本相符.该方法所需样品量仅为索氏抽提的1/10,且高效、快速、无污染和危险,可用于少量特殊地质样品中生物标志化合物的萃取分析.