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 (Pchlide) 氧化还原酶催化叶绿素 a 生物合成的倒数第二步大多数含氧光养生物（包括蓝藻）都有两种结构上不相关的 Pchlide 还原酶，即光依赖性 Pchlide 还原酶 (LPOR) 和固氮酶样光非依赖性（暗操作）Pchlide 还原酶。 (DPOR)。在本研究中，我们研究了以下两个方面； 1) 荚膜红杆菌 DPOR 的生化特性，2) DPOR 和 LPOR 响应蓝藻中光和氧水平环境变化的功能分化。1) 我们证明了荚膜红杆菌 DPOR 的一些基本特性 Pchlide 的 Km 值。为 10.6 μM。铁氧还蛋白在凝胶过滤中充当 DPOR 的电子供体。色谱分析表明L-蛋白和NB-蛋白分别是同二聚体[(BchL)_2]和异四聚体[(BchN)_2(BchB)_2]。2)缺乏LPOR的蓝藻光自养生长的最大氧水平。确定了突变体，其中 DPOR 是唯一的 Pchlide 还原酶，我们建议氧含量 (3% v/v)。 “叶绿素巴斯德点”是从在厌氧室中在高光通入氮气（含有20 CO_2）的情况下生长的缺乏LPOR的突变细胞制备的，在ATP依赖性的可溶性级分中成功地检测到了DPOR活性。首次暴露于空气中后，DPOR 活性显着降低，半衰期约为 15 分钟，与 DPOR 的半衰期相当。该结果表明，蓝藻等产氧光养生物已经进化出一些保护 DPOR 免受氧气侵害的机制。