. "Edited: May, B, 2011-03-24"^^ . "Authored: May, B, 2011-03-24"^^ . "Reviewed: Jassal, B, 2012-04-27"^^ . "Carbonic anhydrase IV (CA4) anchored to extracellular face of the plasma membrane (Wistrand et al. 1999) hydrates carbon dioxide (CO2) to yield bicarbonate (HCO3-) and a proton (H+) (Zhu & Sly 1990, Okayuma et al. 1992, Baird et al. 1997, Innocenti et al. 2004). During the reaction a hydroxyl group bound by the zinc ion (Zn2+) of CA4 attacks the CO2 molecule to directly form HCO3- (reviewed in Lindskog 1997). The HCO3- is displaced by water, which is then deprotonated by a histidine residue to recreate the Zn2+:hydroxyl group. Depending on the concentrations of reactants the reaction is reversible."^^ . . . . . . . . . . . "H2O + CO2 -> H+ + HCO3-"^^ . "Carbonic Anhydrase IV Hydrates Carbon Dioxide to Form a Proton and Bicarbonate"^^ . "4.2.1.1"^^ . . . . .