Studies on Mg-releasing Enzyme, Chlorophyllide-Mg-Dechelatase.

研究了白色鹅掌粗提物中叶绿素（Chl）在黑暗条件下的降解。脱镁叶绿酸a的衍生物形成时，叶绿素a或叶绿素a与脱色的粗提物温育。脱镁叶绿酸的形成被完全防止通过热处理的提取物，表明该反应是酶促的，并且假设存在镁释放酶，即所谓的镁脱螯合酶。这一假设得到了以下观察结果的有力支持：脱镁叶绿酸的形成被10 mM MgCl抑制了51%。通过高效薄层色谱（HPTLC）和液相色谱（HPLC）分析表明，叶绿素a、脱镁叶绿酸a、13 -羟基叶绿素a和焦脱镁叶绿酸a的出现伴随着叶绿素a水平的降低。看来，叶绿素降解的粗提物的C。叶绿素a -叶绿素a -脱镁叶绿酸a-焦脱镁叶绿酸a在叶绿素分解的途径中，脱镁叶绿酸的积累不是由于缺乏酶和/或辅因子，而是可以解释为在脱镁叶绿酸衍生物形成的远端步骤的部分抑制，这导致脱镁叶绿酸种类的积累。有关叶绿素降解的酶的纯化和表征正在进行中。

The breakdown of chlorophyll (Chl) in crude extracts of Chenopodium album (white goose foot) in the dark was examined. Derivatives of pheophorbide a were formed when chlorophyll a or chlorophyllide a was incubated with depigmented crude extracts. The formation of pheophorbide was completely prevented by heat treatment of extracts, indicating that the reaction was enzymatic, and the presence of a Mg-releasing enzyme, the so called Mg-dechelatase, was postulated. This hypothesis was strongly supported by the observation that the formation of pheophorbide was inhibited by 51% by 10mM MgCl. Analysis by High-Performance Thin-Layer Chromatography (HPTLC) and liquid chromatography (HPLC) showed that the appearance of chlorophyllide a, pheophorbide'a, 13 -hydroxychlorophyllide a and pyropheophorbide a was accompanied by a concomitant decrease in levels of Chl a. It appears that Chl is degraded in a crude extract of C. album via the following enzymatically catalyzed reactions : Chl a ---- chlorophyllide a ---- pheophorbide a ---- pyropheophorbide a In the pathway of Chl breakdown, an accumulation of pheophorbide is not due to a lack of enzymes adn/or cofactors but may be explained by partial inhibition at the step distal to formation of pheophorbide derivatives which results in the accumulation of pheophorbide species. The purification and characterization of enzymes concerning the degradation of Chl are now in progress.