Chen A, Poulter C D
Department of Chemistry, University of Utah, Salt Lake City 84112.
J Biol Chem. 1993 May 25;268(15):11002-7.
Farnesyl diphosphate (FPP)/geranylgeranyl diphosphate (GGPP) synthase, a bifunctional enzyme that synthesizes C15 and C20 isoprenoid diphosphates from isopentenyl diphosphate and dimethylallyl diphosphate, was purified to homogeneity from the archaebacterium Methanobacterium thermoautotrophicum. The only activities detected from synthesis of FPP and GGPP copurified through (NH4)2SO4 precipitation and four chromatographic steps. The pure enzyme was a 79-kDa homodimer that catalyzed the sequential addition of isopentenyl diphosphate to dimethylallyl diphosphate, geranyl diphosphate, and FPP by a non-processive mechanism which allowed substantial amounts of FPP to accumulate during turnover, creating a pool for further elongation to GGPP or for synthesis of squalene. The bifunctional enzyme required Mg2+ or Mn2+ and was optimally active at 65 degrees C. Catalysis of chain elongation in M. thermoautotrophicum differs from related reactions in eubacteria and eukaryotes, where distinct FPP synthases and GGPP synthases are found.
法尼基二磷酸（FPP）/香叶基香叶基二磷酸（GGPP）合酶是一种双功能酶，可从异戊烯基二磷酸和二甲基烯丙基二磷酸合成C15和C20类异戊二烯二磷酸，它从古细菌嗜热自养甲烷杆菌中纯化至同质。从FPP和GGPP合成中检测到的唯一活性通过硫酸铵沉淀和四个色谱步骤共纯化。纯酶是一种79 kDa的同型二聚体，通过非连续机制催化异戊烯基二磷酸依次添加到二甲基烯丙基二磷酸、香叶基二磷酸和FPP上，这种机制允许在周转过程中积累大量FPP，形成一个池，用于进一步延伸至GGPP或用于角鲨烯的合成。这种双功能酶需要Mg2+或Mn2+，在65℃时活性最佳。嗜热自养甲烷杆菌中链延伸的催化作用不同于真细菌和真核生物中的相关反应，在真细菌和真核生物中发现了不同的FPP合酶和GGPP合酶。
