Abstract: Due to the absence of detailed kinetic parameters，one of the most important methods，network topology based metabolic pathway analysis has been developed.The paper firstly introduces the brief history of network based on pathway analysis.Then，two such network based methods are emphasized：Elementary modes and extreme pathways，with their similarities，differences and applications.At last，extreme pathways are employed to analyze PHB metabolism of B.thuringiensis.Except for “historical” biochemical pathways，the results also suggest that there are some novel pathways.

Key words: metabolic network, metabolic pathway, elementary modes, extreme pathways

摘要： 由于缺乏详尽的热力学参数，基于网络拓扑的代谢途径分析是现阶段最重要的途径分析方法。首先简单地介绍了基于网络的途径分析方法发展简史，随后着重说明了基于凸分析的两种代谢途径分析方法：基元模式和极端途径及它们之间的异同，并详细阐述了这两种方法的具体应用。最后，使用极端途径分析了苏云金杆菌的PHB代谢。结果表明，除了传统的途径，还存在一些新颖的途径可用于PHB合成。

关键词: 代谢网络, 代谢途径, 基元模式, 极端途径