Quantification of the Contribution of CO2, HCO3-, and External Carbonic Anhydrase to Photosynthesis at Low Dissolved Inorganic Carbon in Chlorella saccharophila
Quantification of the Contribution of CO2, HCO3-, and External Carbonic Anhydrase to Photosynthesis at Low Dissolved Inorganic Carbon in Chlorella saccharophila
复制标题
定量分析 CO2、HCO3- 和外部碳酸酐酶在低溶解无机碳条件下对糖小球藻光合作用的贡献
作者：
T. Williams;B. Colman
结合CO2和HCO3的全细胞速率常数，建立了一个方程，它准确地描述了低溶解无机碳条件下单细胞藻类悬浮液中的光合作用。在pH值为8.0时，藻类细胞可利用的二氧化碳浓度取决于细胞对HCO3-的供应和损失以及细胞对HCO3-的利用率。在细胞密度增加(>；30 mg叶绿素[Chl]L-1)时，细胞对二氧化碳的利用很高，由于单独使用HCO3，绝对PHS对Chl浓度的曲线图的斜率接近以毫克Chl为基础的PHS的速率。PHs对HCO3-的斜率为HCO3-的速率常数，嗜糖小球藻的斜率为0.16 L mg-1Chlh-1。溶解无机碳的常数(在有外部碳酸酐酶的细胞中测量)和HCO3-1的常数之差是二氧化碳的常数，为26 L mg-1Chl h-1。这种差异导致PHS的半饱和常数在高单元密度下增加了5-6倍。由外源碳酸酐酶引起的二氧化碳使用量的增加在数学上被描述为细胞密度的函数。
An equation has been developed incorporating whole-cell rate constants for CO2 and HCO3- that describes accurately photosynthesis (Phs) in suspensions of unicellular algae at low dissolved inorganic carbon. At pH 8.0 the concentration of CO2 available to the algal cells depends on the rate of supply from, and the loss to, HCO3- and the rate of use by the cells. At elevated cell densities (>30 mg chlorophyll [Chl] L-1), at which CO2 use by the cells is high, the slope of a graph of absolute Phs versus Chl concentration approaches the rate of Phs on a milligram of Chl basis because of HCO3- use alone. The slope of a graph of Phs versus HCO3- will be the rate constant for HCO3-, and for Chlorella saccharophila it was 0.16 L mg-1 Chl h-1. The difference between the constants for dissolved inorganic carbon (measured in cells with external carbonic anhydrase) and HCO3-1 is the constant for CO2, which was 26 L mg-1 Chl h-1. This difference causes the half-saturation constant for Phs to increase 5- to 6-fold at high cell densities. The increase in CO2 use as a result of external carbonic anhydrase is described mathematically as a function of cell density.