权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

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.

原叶绿素氧化还原酶催化叶绿素a生物合成的倒数第二步。大多数光养生物包括蓝细菌具有两种结构上不相关的Pchlide还原酶，光依赖性Pchlide还原酶（LPOR）和固氮酶样光非依赖性（暗操作）Pchlide还原酶（DPOR）。本研究从以下两个方面进行了研究：1）荚膜红细菌DPOR的生化特性; 2）蓝藻DPOR和LPOR在光氧环境变化下的功能分化。Pchlide的Km值为10.6 μM。铁氧还蛋白是DPOR的电子供体。凝胶过滤层析洗脱图谱表明，L蛋白和NB蛋白分别为同源二聚体[（BchL）_2]和异源四聚体[（BchN）_2（BchB）_2]。2）测定了一株LPOR缺失突变体（DPOR是唯一的Pchlide还原酶）光合自养生长的最大氧浓度。我们提出了氧气水平（3% v/v）的“叶绿素巴斯德点”。在无氧室中，用氮气（含20 CO_2）在强光下鼓泡生长的LPOR缺失突变体细胞制备可溶性组分。首次在可溶性组分中以ATP依赖的方式成功检测到DPOR活性。暴露于空气中后，DPOR活性急剧下降，半衰期约为15分钟，这是与来自R. capsulatus的DPOR相当。这一结果表明，产氧光合生物，如蓝藻已经进化出一些机制，以保护DPOR从氧气。