Carbonic anhydrase dehydrates bicarbonate (plasma membrane)

Carbonic anhydrase IV (CA4, Zhu and Sly 1990, Okuyama et al. 1992, Baird et al. 1997, Innocenti et al. 2004), carbonic anhydrase IX (CA9, Wingo et al. 2001, Hilvo et al. 2008), carbonic anhydrase XII (CA12, Ulmasov et al. 2000, Pastorekova et al. 2008), and carbonic anhydrase XIV (CA14, Ozensoy et al. 2005, Temperini et al. 2008) are membrane-bound enzymes that dehydrate bicarbonate to yield water and carbon dioxide. Depending on the concentrations of reactants the reaction is reversible.<br>CA4 has high catalytic activity. CA9, CA12, and CA14 have moderate activity. CA4 is anchored to the extracellular face of the plasma membrane by glycosylphosphatidylinositol. CA9, CA12, and CA14 are single-pass transmembrane proteins. CA4 is found on the extracellular face of capillaries in kidney, lung, and muscle where it maintains the gradient of carbon dioxide between tissue and blood. CA9 and CA12 are found on basolateral membranes of epithelia. CA9 is inducible by Hypoxia-inducible factor 1 alpha (HIF1alpha) and acidifies the extracellular environment of tumors. In rodents CA15 is membrane anchored and has low activity; in primates CA15 is a pseudogene.

碳酸酐酶IV（CA4，Zhu和Sly，1990年；Okuyama等人，1992年；Baird等人，1997年；Innocenti等人，2004年），碳酸酐酶IX（CA9，Wingo等人，2001年；Hilvo等人，2008年），碳酸酐酶XII（CA12，Ulmasov等人，2000年；Pastorekova等人，2008年），以及碳酸酐酶XIV（CA14，Ozensoy等人，2005年；Temperini等人，2008年）均为膜结合酶，其功能为将碳酸氢盐脱水，产生水和二氧化碳。该反应的可逆性取决于反应物的浓度。CA4具有高催化活性。CA9、CA12和CA14则表现出中等活性。CA4通过糖基磷脂酰肌醇（Glycosylphosphatidylinositol）锚定于质膜的外细胞面。CA9、CA12和CA14为单次穿膜蛋白。CA4存在于肾脏、肺和肌肉的毛细血管外细胞面，维持组织与血液间二氧化碳的梯度。CA9和CA12存在于上皮细胞的基底外侧膜上。CA9可被缺氧诱导因子1α（HIF1alpha）诱导，并酸化肿瘤的细胞外环境。在啮齿动物中，CA15为膜锚定且活性较低；而在灵长类动物中，CA15则为伪基因。