Gros G, Moll W, Hoppe H, Gros H
J Gen Physiol. 1976 Jun;67(6):773-90. doi: 10.1085/jgp.67.6.773.
We have measured CO2 fluxes across phosphate solutions at different carbonic anhydrase concentrations, bicarbonate concentration gradients, phosphate concentrations, and mobilities. Temperature was 22-25 degrees C, the pH of the phosphate solutions was 7.0-7.3. We found that under physiological conditions of pH and pCO2 a facilitated diffusion of CO2 occurs in addition to free diffusion when (a) sufficient carbonic anhydrase is present, and (b) a concentration gradient of HCO3- is established along with a pCO2 gradient, and (c) the phosphate buffer has a mobility comparable to that of bicarbonate. When the phosphate was immobilized by attaching 0.25-mm-long cellulose particles, no facilitation of CO2 diffusion was detectable. A mechanism of facilitated CO2 diffusion in phosphate solutions analogous to that in albumin solutions was proposed on the basis of these findings: bicarbonate diffusion together with a facilitated proton transport by phosphate diffusion. A mathematical model of this mechanism was formulated. The CO2 fluxed predicted by the model agree quantitatively with the experimentally determined fluxes. It is concluded that a highly effective proton transport mechanism acts in solutions of mobile phosphate buffers. By this mechanism; CO2 transfer may be increased up to fivefold and proton transfer may be increased to 10,000-fold.
我们测量了在不同碳酸酐酶浓度、碳酸氢盐浓度梯度、磷酸盐浓度和迁移率条件下，穿过磷酸盐溶液的二氧化碳通量。温度为22 - 25摄氏度，磷酸盐溶液的pH值为7.0 - 7.3。我们发现，在pH值和二氧化碳分压的生理条件下，当（a）存在足够的碳酸酐酶，（b）建立起碳酸氢根浓度梯度以及二氧化碳分压梯度，并且（c）磷酸盐缓冲液的迁移率与碳酸氢盐的迁移率相当的时候，除了自由扩散外，还会发生二氧化碳的易化扩散。当通过附着0.25毫米长的纤维素颗粒使磷酸盐固定化时，未检测到二氧化碳扩散的促进作用。基于这些发现，提出了一种在磷酸盐溶液中类似于白蛋白溶液中的二氧化碳易化扩散机制：碳酸氢根扩散与通过磷酸盐扩散促进的质子转运一起。构建了该机制的数学模型。该模型预测的二氧化碳通量与实验测定的通量在数量上相符。得出的结论是，在可移动的磷酸盐缓冲液溶液中存在一种高效的质子转运机制。通过这种机制，二氧化碳的转移可能会增加到五倍，质子转移可能会增加到10000倍。
