Fridlyand L E, Kaler V L
V. F. Kuprevich Institute of Experimental Botany, Academy of Sciences of the Belorussian SSR, Minsk.
Gen Physiol Biophys. 1987 Dec;6(6):617-36.
The possibility of a specific CO2 concentrating mechanism present in chloroplasts of C3 plants is analyzed. Proton gradient between thylakoids and the stroma is assumed to be the driving force for this process. The possible CO2 concentrating mechanisms are: 1. HCO3- permeation into thylakoids, its dehydration there and diffusion of CO2 formed into the stroma; 2. Dehydration of HCO3- present in the stroma at the thylakoid surface in a reaction with H+ leaving the thylakoids through: a) channels of membrane-bound carbonic anhydrase; b) channels of the ATPase complex. A system of equations describing CO3- and CO2 diffusion as well as CO2 assimilation and formation was used. The increase in photosynthesis rate, upon CO2 diffusion being facilitated in the presence of carbonic anhydrase, and due to the action of CO2 concentrating mechanisms, was numerically estimated. The CO2 concentrating mechanism was shown to function effectively only with the entire chloroplast being the CO2 concentrating zone. This is the case when the bulk of stromal carbonic anhydrase is localized near the inner chloroplast envelope. The existence of CO2 concentrating mechanisms around a single granum or around thylakoids is hardly possible. Approaches enabling the detection of similar concentrating mechanisms are discussed.
分析了C3植物叶绿体中存在特定二氧化碳浓缩机制的可能性。类囊体与基质之间的质子梯度被认为是这一过程的驱动力。可能的二氧化碳浓缩机制有：1. HCO3-渗透到类囊体中，在其中脱水并使形成的CO2扩散到基质中；2. 基质中存在于类囊体表面的HCO3-与通过以下方式离开类囊体的H+反应脱水：a) 膜结合碳酸酐酶的通道；b) ATP酶复合体的通道。使用了一个描述CO3-和CO2扩散以及CO2同化和形成的方程组。对在碳酸酐酶存在下促进CO2扩散以及由于二氧化碳浓缩机制的作用而导致的光合作用速率增加进行了数值估算。结果表明，只有当整个叶绿体作为二氧化碳浓缩区时，二氧化碳浓缩机制才能有效发挥作用。当大部分基质碳酸酐酶位于叶绿体内膜附近时就是这种情况。围绕单个基粒或类囊体存在二氧化碳浓缩机制几乎是不可能的。讨论了能够检测类似浓缩机制的方法。
