Takei K, Sakakibara H, Sugiyama T
Department of Biological Mechanisms and Functions, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
J Biol Chem. 2001 Jul 13;276(28):26405-10. doi: 10.1074/jbc.M102130200. Epub 2001 Apr 19.
The initial step in the de novo biosynthesis of cytokinin in higher plants is the formation of isopentenyladenosine 5'-monophosphate (iPMP) from AMP and dimethylallylpyrophosphate (DMAPP), which is catalyzed by adenylate isopentenyltransferase (IPT). Although cytokinin is an essential hormone for growth and development, the nature of the enzyme for its biosynthesis in higher plants has not been identified. Herein, we describe the molecular cloning and biochemical identification of IPTs from Arabidopsis thaliana. Eight cDNAs encoding putative IPT, designated as AtIPT1 to AtIPT8, were picked up from A. thaliana. The Escherichia coli transformants expressing the recombinant proteins excreted cytokinin species into the culture medium except for that expressing AtIPT2 that is a putative tRNA IPT. A purified recombinant AtIPT1 catalyzed the formation of iPMP from DMAPP and AMP. These results indicate that the small multigene family contains both types of isopentenyltransferase, which could synthesize cytokinin and mature tRNA.
高等植物中细胞分裂素从头生物合成的第一步是由腺苷酸异戊烯基转移酶（IPT）催化，从AMP和二甲基烯丙基焦磷酸（DMAPP）形成异戊烯基腺苷5'-单磷酸（iPMP）。尽管细胞分裂素是生长和发育所必需的激素，但高等植物中其生物合成酶的性质尚未确定。在此，我们描述了来自拟南芥的IPT的分子克隆和生化鉴定。从拟南芥中筛选出八个编码假定IPT的cDNA，命名为AtIPT1至AtIPT8。除了表达假定的tRNA IPT即AtIPT2的大肠杆菌转化体之外，表达重组蛋白的大肠杆菌转化体将细胞分裂素种类分泌到培养基中。纯化的重组AtIPT1催化从DMAPP和AMP形成iPMP。这些结果表明，这个小的多基因家族包含两种类型的异戊烯基转移酶，它们可以合成细胞分裂素和成熟的tRNA。
