Maren T H, Rayburn C S, Liddell N E
Science. 1976 Feb 6;191(4226):469-72. doi: 10.1126/science.813299.
The hydration rate of CO2 catalyzed by human red cell carbonic anhydrase B is 92 percent reduced by the normal concentrations of chloride and bicarbonate in red cells. This reflects a general sensitivity of this reaction to halides and other anions, up to 87 times greater than the effect on red cell carbonic anhydrase C. The catalytic hydration of CO2 is generally more (up to 24 times) sensitive to inhibition by anions and sulfonamides than the dehydration of HCO3-, probably reflecting different mechanisms. The sensitivity of enzyme B to anion inhibition also depends upon the substrate, being much greater for CO2 than for certain esters. On the basis of the very low catalytic activity of B for CO2 in the presence of physiological concentration of chloride, and the fact that carbonic anhydrase C is effective for CO2 hydration (in the presence of chloride) at a rate 340 times greater than that of CO2 output from tissues, it appears that the biological role of enzyme B is not that of a carbonic anhydrase.
人红细胞碳酸酐酶B催化的二氧化碳水合速率，会因红细胞中正常浓度的氯离子和碳酸氢根离子而降低92%。这反映出该反应对卤化物和其他阴离子具有普遍敏感性，其敏感性比红细胞碳酸酐酶C所受影响大87倍。一般而言，二氧化碳的催化水合作用对阴离子和磺胺类药物抑制作用的敏感性更高（高达24倍），比碳酸氢根离子的脱水作用更敏感，这可能反映了不同的机制。酶B对阴离子抑制的敏感性还取决于底物，对二氧化碳的敏感性比对某些酯类要高得多。鉴于在生理浓度的氯离子存在下，酶B对二氧化碳的催化活性非常低，且碳酸酐酶C在有氯离子存在时对二氧化碳水合作用的效率比组织中二氧化碳输出速率高340倍，因此酶B的生物学作用似乎并非作为一种碳酸酐酶。
