Paseshnichenko V A
Bakh Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 117071 Russia.
Biochemistry (Mosc). 1998 Feb;63(2):139-48.
Data concerning the discovery of an alternative non-mevalonate pathway for isoprenoid biosynthesis leading to isopentenyl diphosphate formation are reviewed. This pathway has been discovered in experiments with several eubacteria producing triterpenoids of the hopane series. 13C-labeled acetate, glucose, and triose phosphates were used as precursors. The 13C-labeling patterns in isoprenoids were studied by 13C-NMR spectrometry. In eubacteria the universal C5 precursor--isopentenyl diphosphate--did not appear to form via the classical acetate/mevalonate pathway, but via a novel glyceraldehyde 3-phosphate/pyruvate pathway. It is postulated that the condensation of the C2 unit formed as a result of pyruvate decarboxylation with the C3 unit (glyceraldehyde 3-phosphate) and the next transposition leads to the formation of the branched C5 precursor--isopentenyl diphosphate. In Scenedesmus obliquus not only all plastid isoprenoids (carotenoids and prenyl side chains of chlorophylls and plastoquinone-9) were formed via this novel pathway, but also the non-plastid cytoplasmic sterols. In higher plants the plastid isoprenoids were formed via the glyceraldehyde 3-phosphate/pyruvate pathway, while the cytoplasmic sterols were formed via the acetate/mevalonate pathway.
本文综述了关于类异戊二烯生物合成中导致异戊烯基二磷酸形成的另一条非甲羟戊酸途径的发现的数据。这条途径是在对几种产生藿烷系列三萜类化合物的真细菌进行的实验中发现的。使用13C标记的乙酸盐、葡萄糖和磷酸丙糖作为前体。通过13C核磁共振光谱研究了类异戊二烯中的13C标记模式。在真细菌中，通用的C5前体——异戊烯基二磷酸——似乎不是通过经典的乙酸盐/甲羟戊酸途径形成的，而是通过一条新的3-磷酸甘油醛/丙酮酸途径形成的。据推测，丙酮酸脱羧形成的C2单元与C3单元（3-磷酸甘油醛）缩合，随后的转位导致形成支链C5前体——异戊烯基二磷酸。在斜生栅藻中，不仅所有质体类异戊二烯（类胡萝卜素以及叶绿素和质体醌-9的异戊烯基侧链）都是通过这条新途径形成的，而且非质体细胞质甾醇也是如此。在高等植物中，质体类异戊二烯通过3-磷酸甘油醛/丙酮酸途径形成，而细胞质甾醇则通过乙酸盐/甲羟戊酸途径形成。
