The Biochemistry and Molecular Biology of Isoprenoid Metabolism

摘要: The term isoprenoid is an older that has been given a renewed use in the last 8 to 10 years describe fascinating family of compounds derived from isoprene building block. Earlier, investigators referred this as terpenes or terpenoids, terms related turpentine oils used elucidating chemical structures isoprenoids 1800s. One can also find numerous references particular classes such monoterpenes sterols, referring investigative approaches often focused on only single compound. However, recent results have revealed surprising similarities among branch-point enzymes responsible for directing carbon flow away central portion biochemical pathway, and others suggested understanding regulation one branch pathway may involve coordination intracellular localization other portions well. These provocative findings interrelatedness, which will be discussed more fully below, argue inclusive "isoprenoids" now seems descriptive pathway. Plant comprise structurally diverse group divided into primary secondary metabolites (Fig. 1). Isoprenoids are include carotenoids, growth regulators, polyprenol substituents dolichols, quinones, proteins. essential membrane integrity, photoprotection, orchestration developmental programs, anchoring functions specific systems, respectively. classified monoterpenes, sesquiterpenes, diterpenes. Compounds within latter category considered because they not viability. mediate important interactions between plants their environment. For example, terpenoids correlated with plant-plant (Stevens, 1984), plantinsect (Gibson Pickett, 1983), plant-pathogen (Stoessl et al., 1976) interactions. biosynthetic sometimes mevalonate textbooks. From technical viewpoint, makes sense. Mevalonate six-carbon intermediate arising sequential condensation three acetyl-CoA units generate HMG-CoA, converted irreversible reaction catalyzed by HMG-CoA reductase (HMGR). Due nature reaction, early workers correctly surmised step was likely regulatory point sterol biosynthesis mammalian systems eventually absolute rate cholesterol level enzyme activity (Goldstein Brown, 1990). Whether plays similar rate-limiting role controlling plant remains unresolved (Bach, 1986; Narita Gruissem, 1989; Choi 1992). sequentially phosphorylated decarboxylated IPP, along dimethylallyl diphosphate, interconvertible isomer represent "activated" monomer blocks all isoprenoids. Condensation diphosphate IPP head-to-tail fashion generates GPP; addition second unit FPP; third GGPP; so on. polymerization reactions prenyltransferases direct attack carbocation (an electron-deficient atom resulting loss moiety substrate) electron-rich double bond molecule 2). electrophilic these unusual relative general nucleophilic condensations occurring pathways, but appears common mechanism especially those catalyzing cyclization various intermediates (Gershenzon Croteau, 1993). GPP, FPP, GGPP monoterpene, sesquiterpene, diterpene synthases cyclases committing end products 1 Work author's laboratory metabolism supported National Science Foundation. This journal article 94-3-195 Kentucky Agricultural Experiment Station. * E-mail chappell@ukcc.uky.edu; fax 1-606-323-1952. Abbreviations: farnesyl diphosphate; GGPP, geranylgeranyl geranyl 3-hydroxy-3-methylglutaryl coenzyme A; HMGR, reductase; isopentenyl diphosphate.