Coordinated evolution of oxygenic photosynthesis and chlorophyll biosynthesis

含氧光合作用和叶绿素生物合成的协调进化

基本信息

批准号：
15570033
负责人：
FUJITA Yuichi
金额：
$ 2.43万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

Protochlorophyllide (Pchlide) oxidoreductase catalyzes the penultimate step of chlorophyll a biosynthesis. Most oxygenic phototrophs including cyanobacteria have two structurally unrelated Pchlide reductases, a light-dependent Pchlide reductase(LPOR) and a nitrogenase-like light-independent (dark-operative) Pchlide reductase (DPOR). In this study, we investigate the following two aspects ; 1)biochemical properties of DPOR from Rhodobacter capsulatus, and 2)functional differentiation of DPOR and LPOR in response to environmental changes of light and oxygen levels in cyanobacteria.1)We demonstrated some basic properties of DPOR from Rhodobacter capsulatus. The Km value for Pchlide was 10.6 μM. Ferredoxin functioned as an electron donor to DPOR. Elution profiles in gel filtration chromatography indicated that L-protein and NB-protein are a homodimer [(BchL)_2] and a heterotetramer [(BchN)_2(BchB)_2], respectively. 2)A maximal oxygen level for photoautotrophic growth of a cyanobacterial LPOR-lacking mutant, in which DPOR is the sole Pchlide reductase, was determined. We propose the oxygen level (3% v/v) "Chlorophyll Pasteur point". A soluble fraction was prepared from the LPOR-lacking mutant cells grown under high light bubbling with nitrogen (containing 20 CO_2) in an anaerobic chamber. The DPOR activity was successfully detected in the soluble fraction in an ATP-dependent manner for the first time. Upon exposure to the air, the DPOR activity was drastically decreased with a half-life of approximately 15 min, which was comparable with that of DPOR from R.capsulatus. This result suggests that oxygenic phototrophic organisms such as cyanobacteria have evolved some mechanisms to protect DPOR from oxygen.

原氯叶酸酯（Pchlide）氧化氧化激酶催化叶绿素A生物合成的倒数第二步。包括蓝细菌在内的大多数氧气光颗粒具有两个结构无关的PCHLIDE还原，一个依赖于光的Pchlide还原酶（LPOR）和一个硝基化酶样光（深色依赖性（深色）PCHLIDE还原（DPOR）。在这项研究中，我们研究了以下两个方面。 1）DPOR的生物化学特性和2）DPOR和LPOR的功能分化响应于蓝细菌中光和氧水平的环境变化。1）我们证明了DPOR与Rhodobacter capsulatus的一些基本特性。 Pchlide的KM值为10.6μm。铁蛋白充当DPOR的电子供体。凝胶过滤色谱法中的洗脱曲线表明，L蛋白和NB蛋白分别是同型二聚体[（BCHL）_2]和杂摄影剂[（BCHN）_2（BCHB）_2]。 2）确定了蓝细菌LPOR-Staking突变体的光自营养生长的最大氧气水平，其中DPOR是唯一的Pchlide还原。我们提出氧气水平（3％V/V）“叶绿素粘液液点”。从在厌氧室内用氮气（含有20 co_2）在高光起泡下生长的LPOR-LAKENT突变细胞制备了实体分数。首次以ATP依赖性方式成功地检测了DPOR活性。暴露于空气后，DPOR活性以大约15分钟的半衰期大大改善，与r.capsulatus的DPOR相当。该结果表明，诸如蓝细菌之类的含氧量光养生已经发展了一些保护DPOR免受氧气的机制。