Suzuki Takuo, Masuda Tatsuru, Singh Davinder Pal, Tan Fui-Ching, Tsuchiya Tohru, Shimada Hiroshi, Ohta Hiroyuki, Smith Alison G, Takamiya Ken-ichiro
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8501 Japan.
J Biol Chem. 2002 Feb 15;277(7):4731-7. doi: 10.1074/jbc.M105613200. Epub 2001 Oct 23.
Ferrochelatase catalyzes the insertion of Fe(2+) into protoporphyrin IX to generate protoheme. In higher plants, there is evidence for two isoforms of this enzyme that fulfill different roles. Here, we describe the isolation of a second ferrochelatase cDNA from cucumber (CsFeC2) that was less similar to a previously isolated isoform (CsFeC1) than it was to some ferrochelatases from other higher plants. In in vitro import experiments, the two cucumber isoforms showed characteristics similar to their respective ferrochelatase counterparts of Arabidopsis thaliana. The C-terminal region of CsFeC2 but not CsFeC1 contained a conserved motif found in light-harvesting chlorophyll proteins, and CsFeC2 belonged to a phylogenetic group of plant ferrochelatases containing this conserved motif. We demonstrate that CsFeC2 was localized predominantly in thylakoid membranes as an intrinsic protein, and forming complexes probably with the C-terminal conserved motif, but a minor portion was also detected in envelope membranes. CsFeC2 mRNA was detected in all tissues and was light-responsive in cotyledons, whereas CsFeC1 mRNA was detected in nonphotosynthetic tissues and was not light-responsive. Interestingly, tissue-, light-, and cycloheximide-dependent expressions of the two isoforms of ferrochelatase were similar to those of two glutamyl-tRNA reductase isoforms involved in the early step of tetrapyrrole biosynthesis, suggesting the existence of distinctly controlled tetrapyrrole biosynthetic pathways in photosynthetic and nonphotosynthetic tissues.
亚铁螯合酶催化Fe(2+)插入原卟啉IX中以生成原血红素。在高等植物中，有证据表明该酶的两种同工型发挥着不同的作用。在此，我们描述了从黄瓜中分离出的第二个亚铁螯合酶cDNA（CsFeC2），它与先前分离出的同工型（CsFeC1）的相似性低于其与其他高等植物的一些亚铁螯合酶的相似性。在体外导入实验中，黄瓜的这两种同工型表现出与其拟南芥各自的亚铁螯合酶对应物相似的特征。CsFeC2的C末端区域而非CsFeC1的C末端区域含有在捕光叶绿素蛋白中发现的保守基序，并且CsFeC2属于含有该保守基序的植物亚铁螯合酶的一个系统发育组。我们证明CsFeC2主要定位于类囊体膜中作为一种内在蛋白，并可能通过C末端保守基序形成复合物，但在包膜膜中也检测到一小部分。在所有组织中均检测到CsFeC2 mRNA，并且在子叶中对光有响应，而CsFeC1 mRNA在非光合组织中检测到且对光无响应。有趣的是，亚铁螯合酶的两种同工型的组织、光和环己酰亚胺依赖性表达与参与四吡咯生物合成早期步骤的两种谷氨酰 - tRNA还原酶同工型的表达相似，这表明在光合和非光合组织中存在明显受控的四吡咯生物合成途径。
