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.
利用含有异源表达酶的大肠杆菌裂解物,在体外检测了绿色
硫光合细菌 Chlorobaculum tepidum 中 CT1610
基因编码的一种酶的活性,该酶被注释为
细菌叶绿素(BChl)a 合成酶 BchG(表示为 tepBchG)。在 tepBchG 的存在下,由
细菌叶绿素(BChlide)a 和
焦磷酸香叶酰基生成了在 17-
丙酸残基上具有香叶酰基的 BChl a(BChl aGG)。令人惊讶的是,tepBchG 与 BChl aGG 的酶法生产过程一样,催化形成了带有法呢基的 BChl a(BChl aF),这表明 tepBchG 对异丙基
焦磷酸盐的识别能力较弱。这些结果证实,tepBchG 在 Cba. tepidum 中无疑是 BChl a 的合成酶。在 45 ℃ 时,tepBchG 的酶活性高于
水合根红杆菌的 BchG,但在 35 ℃ 以下时,前者的酶活性低于后者。