Saga Yoshitaka, Hirota Keiya, Harada Jiro, Tamiaki Hitoshi
†Department of Chemistry, Faculty of Science and Engineering, Kinki University, Higashi-Osaka, Osaka 577-8502, Japan.
‡PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan.
Biochemistry. 2015 Aug 18;54(32):4998-5005. doi: 10.1021/acs.biochem.5b00311. Epub 2015 Aug 10.
The activity of an enzyme encoded by the CT1610 gene in the green sulfur photosynthetic bacterium Chlorobaculum tepidum, which was annotated as bacteriochlorophyll (BChl) a synthase, BchG (denoted as tepBchG), was examined in vitro using the lysates of Escherichia coli containing the heterologously expressed enzyme. BChl a possessing a geranylgeranyl group at the 17-propionate residue (BChl aGG) was produced from bacteriochlorophyllide (BChlide) a and geranylgeranyl pyrophosphate in the presence of tepBchG. Surprisingly, tepBchG catalyzed the formation of BChl a bearing a farnesyl group (BChl aF) as in the enzymatic production of BChl aGG, indicating loose recognition of isoprenoid pyrophosphates in tepBchG. In contrast to such loose recognition of isoprenoid substrates, BChlide c and chlorophyllide a gave no esterifying product upon being incubated with geranylgeranyl or farnesyl pyrophosphate in the presence of tepBchG. These results confirm that tepBchG undoubtedly acts as the BChl a synthase in Cba. tepidum. The enzymatic activity of tepBchG was higher than that of BchG of Rhodobacter sphaeroides at 45 °C, although the former activity was lower than the latter below 35 °C.
对绿硫光合细菌嗜热栖热菌（Chlorobaculum tepidum）中由CT1610基因编码的一种酶（该酶被注释为细菌叶绿素（BChl）a合酶BchG，记为tepbchG）的活性，使用含有异源表达该酶的大肠杆菌裂解物进行了体外检测。在tepbchG存在的情况下，细菌叶绿素a（BChlide）a和香叶基香叶基焦磷酸可产生在17-丙酸残基处带有香叶基香叶基的细菌叶绿素a（BChl aGG）。令人惊讶的是，tepbchG催化生成了带有法尼基的细菌叶绿素a（BChl aF），就如同在BChl aGG的酶促生产过程中一样，这表明tepbchG对类异戊二烯焦磷酸的识别较为宽松。与对类异戊二烯底物的这种宽松识别相反，在tepbchG存在的情况下，将细菌叶绿素c（BChlide c）和叶绿素a与香叶基香叶基焦磷酸或法尼基焦磷酸一起孵育时，未产生酯化产物。这些结果证实，tepbchG无疑在嗜热栖热菌中充当BChl a合酶。在45℃时，tepbchG的酶活性高于球形红杆菌（Rhodobacter sphaeroides）的BchG，不过在35℃以下，前者的活性低于后者。
