Ericsson J, Runquist M, Thelin A, Andersson M, Chojnacki T, Dallner G
Department of Biochemistry, Arrhenius Laboratories for the Natural Sciences, Stockholm University, Sweden.
J Biol Chem. 1993 Jan 15;268(2):832-8.
The present study describes the presence of two different geranylgeranyl diphosphate (GGPP) synthase activities, one cytosolic and one membrane-associated, in a number of rat tissues. Both enzymes utilize farnesyl diphosphate (FPP) and isopentenyl diphosphate (IPP) as substrates, but they give rise to different products. The membrane-associated activity produces trans,trans,cis-(E,E,Z)-GGPP, involved in the biosynthesis of long-chain polyprenols. The cytosolic activity produces only the all-trans-(E,E,E) isomer of GGPP, which is utilized as substrate in cytosolic protein prenylation reactions. All-trans-GGPP synthase activity was recovered in the cytosolic fraction from all tissues investigated, but the specific activities varied. The highest specific activities were found in brain, spleen, and testis, followed by kidney and liver. The enzyme activity in rat brain cytosol was further characterized and found to exhibit a narrow pH optimum around 5.0-6.0 and to be highly stimulated by Zn2+. Maximal stimulation was attained with 1 mM Zn2+, whereas Mg2+ had no effect on the enzyme activity. The all-trans-GGPP synthase activity exhibited high affinities for its substrates, i.e. the apparent Km values for FPP and IPP were found to be 0.6 and 3.5 microM, respectively. When rats were fed mevinolin (lovastatin), FPP and all-trans-GGPP synthase activities were affected differently in certain tissues. Mevinolin treatment resulted in an increase in FPP but a decrease in all-trans-GGPP synthase activity in rat liver and kidney. In spleen mevinolin treatment caused a greater than 70% decrease in all-trans-GGPP synthase activity, while FPP synthase was almost unaffected. The presence of two different GGPP synthase activities in the cell, together with the fact that FPP and all-trans-GGPP synthesis in the cytosol are regulated independently, may be of significance in the regulation of isoprenoid biosynthesis, as well as of protein isoprenylation.
本研究描述了在多种大鼠组织中存在两种不同的香叶基香叶基二磷酸（GGPP）合酶活性，一种存在于胞质溶胶中，另一种与膜相关。两种酶都利用法呢基二磷酸（FPP）和异戊烯基二磷酸（IPP）作为底物，但它们产生不同的产物。与膜相关的活性产生反式、反式、顺式-（E，E，Z）-GGPP，参与长链聚戊烯醇的生物合成。胞质溶胶活性仅产生GGPP的全反式-（E，E，E）异构体，其在胞质溶胶蛋白异戊二烯化反应中用作底物。在所有研究的组织的胞质溶胶部分中均检测到全反式-GGPP合酶活性，但比活性有所不同。在脑、脾和睾丸中发现最高的比活性，其次是肾和肝。对大鼠脑胞质溶胶中的酶活性进行了进一步表征，发现其在pH约为5.0 - 6.0时表现出较窄的最适pH值，并且受到Zn2+的高度刺激。用1 mM Zn2+可达到最大刺激，而Mg2+对酶活性没有影响。全反式-GGPP合酶活性对其底物表现出高亲和力，即FPP和IPP的表观Km值分别为0.6和3.5 microM。当给大鼠喂食美伐他汀（洛伐他汀）时，FPP和全反式-GGPP合酶活性在某些组织中受到不同的影响。美伐他汀处理导致大鼠肝脏和肾脏中FPP增加，但全反式-GGPP合酶活性降低。在脾脏中，美伐他汀处理导致全反式-GGPP合酶活性降低超过70%，而FPP合酶几乎不受影响。细胞中存在两种不同的GGPP合酶活性，以及胞质溶胶中FPP和全反式-GGPP合成受到独立调节这一事实，可能在类异戊二烯生物合成以及蛋白质异戊二烯化的调节中具有重要意义。
