| Summary: | 博士 === 中山醫學大學 === 醫學研究所 === 95 === Purpose :
This dissertation embarks to understand the relationships between nitro compounds and the activation of lipase. Thus, the goal of this study is then to characterize interactions between nitro compounds and Pseudomonas Species lipase (PSL) in vitro.
Results :
PA and styphnic acid are characterized as the mixed-type inhibitors of PSL. From chemical structure point of view, PA and styphnic acid carry hydroxyl groups and make both compounds hydrophilic. Therefore, PA and styphnic acid are capable of entering the hydrophilic active site of Pseudomonas Species lipase and become inhibitors of the enzyme due to the hydrophilic character of both compounds.
On the other hand, TNT, RDX, and HNIW are the essential activators of PSL. From chemical structure point of view, TNT, RDX, and HNIW are more hydrophobic than PA and styphnic acid. Therefore, TNT, RDX, and HNIW presumably mix with triton-X 100 and bind to the co-lipase binding site of PSL and become the essential activators of PSL. Moreover, the interfacial activation of PSL by the essential activators in the presence of detergents is proposed according to the lipase-colipase mechanism. Interestingly, HMX and nitroglycerin are neither an inhibitor nor an activator of the enzyme. Therefore, HMX and nitroglycerin do not bind to the active site of PSL due to the hydrophobic characters of HMX and nitroglycerin. Moreover, HMX does not bind to the co-lipase binding site of PSL probably due to a huge dimension of HMX and weak interactions between HMX and detergent triton X-100. With the glycerol backbone, nitroglycerin has more stable conformations than other nitro compounds and therefore it interacts loosely with the detergent.
Conclusions :
The goal of this work is to determine the enzyme kinetics for Pseudomonas Species lipase catalyzed hydrolysis of substrate p-nitrophenyl butyrate in the presence of nitro compounds such as nitroglycerin, 2,4,6-trinitrotoluene (TNT), picric acid, styphnic acid, hexahydro-1,3,5-trinitrotriazocine (RDX), octahydro-1,3,5,7-tetranitrotriazocine (HMX), and hexanitrohexaazaisowurtzitane (HNIW) in vitro. Kinetically, picric acid and styphnic acid are the mixed-type inhibitors but TNT, RDX, and HNIW are the essential activators of the enzyme in the presence of a detergent triton-X 100. Interestingly, HMX and nitroglycerin are neither an inhibitor nor an activator of the enzyme.
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