Wanke M, Skorupinska-Tudek K, Swiezewska E
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warszawa.
Acta Biochim Pol. 2001;48(3):663-72.
Higher plants, several algae, bacteria, some strains of Streptomyces and possibly malaria parasite Plasmodium falciparum contain the novel, plastidic DOXP/MEP pathway for isoprenoid biosynthesis. This pathway, alternative with respect to the classical mevalonate pathway, starts with condensation of pyruvate and glyceraldehyde-3-phosphate which yields 1-deoxy-D-xylulose 5-phosphate (DOXP); the latter product can be converted to isopentenyl diphosphate (IPP) and eventually to isoprenoids or thiamine and pyridoxal. Subsequent reactions of this pathway involve transformation of DOXP to 2-C-methyl-D-erythritol 4-phosphate (MEP) which after condensation with CTP forms 4-diphosphocytidyl-2-amethyl-D-erythritol (CDP-ME). Then CDP-ME is phosphorylated to 4-diphosphocytidyl-2-amethyl-D-erythritol 2-phosphate (CDP-ME2P) and to 2-C-methyl-D-erythritol-2,4-cyclodiphosphate (ME-2,4cPP) which is the last known intermediate of the DOXP/MEP pathway. For- mation of IPP and dimethylallyl diphosphate (DMAPP) from ME-2,4cPP still requires clarification. This novel pathway appears to be involved in biosynthesis of carotenoids, phytol (side chain of chlorophylls), isoprene, mono-, di-, tetraterpenes and plastoquinone whereas the mevalonate pathway is responsible for formation of sterols, sesquiterpenes and triterpenes. Several isoprenoids were found to be of mixed origin suggesting that some exchange and/or cooperation exists between these two pathways of different biosynthetic origin. Contradictory results described below could indicate that these two pathways are operating under different physiological conditions of the cell and are dependent on the developmental state of plastids.
高等植物、几种藻类、细菌、某些链霉菌菌株以及可能还有疟原虫恶性疟原虫，都含有用于类异戊二烯生物合成的新型质体2-C-甲基-D-赤藓糖醇-4-磷酸/1-脱氧-D-木酮糖-5-磷酸（DOXP/MEP）途径。该途径相对于经典的甲羟戊酸途径而言是替代途径，它始于丙酮酸和3-磷酸甘油醛的缩合，生成1-脱氧-D-木酮糖-5-磷酸（DOXP）；后者产物可转化为异戊烯基二磷酸（IPP），最终转化为类异戊二烯、硫胺素和吡哆醛。该途径随后的反应涉及DOXP转化为2-C-甲基-D-赤藓糖醇-4-磷酸（MEP），MEP与CTP缩合后形成4-二磷酸胞苷-2-C-甲基-D-赤藓糖醇（CDP-ME）。然后CDP-ME磷酸化为4-二磷酸胞苷-2-C-甲基-D-赤藓糖醇-2-磷酸（CDP-ME2P），再转化为2-C-甲基-D-赤藓糖醇-2,4-环二磷酸（ME-2,4cPP），ME-2,4cPP是DOXP/MEP途径最后一个已知的中间体。由ME-2,4cPP形成IPP和二甲基烯丙基二磷酸（DMAPP）的过程仍有待阐明。这条新途径似乎参与了类胡萝卜素、叶绿醇（叶绿素的侧链）、异戊二烯、单萜、二萜、四萜和质体醌的生物合成，而甲羟戊酸途径则负责甾醇、倍半萜和三萜的形成。已发现几种类异戊二烯具有混合来源，这表明这两条不同生物合成来源的途径之间存在一些交换和/或协作。下面所述的相互矛盾的结果可能表明这两条途径在细胞的不同生理条件下发挥作用，并且依赖于质体的发育状态。
