--- title: "Carbonic anhydrase Template – Chemistry Diagram | MolDraw" url: https://www.moldraw.com/templates/enzyme-carbonic-anhydrase/ description: "Carbonic anhydrase template: In carbonic anhydrase II, OH⁻ on Zn²⁺ (held by His94, His96, His119) attacks CO₂ to give Zn-bound HCO₃⁻, which water displaces…" lang: en publisher: Scidart Academy generated: 2026-11-13 --- [MolDraw](https://www.moldraw.com/) › [Templates](https://www.moldraw.com/templates/) › [Biochemistry](https://www.moldraw.com/templates/biochemistry/) › Carbonic anhydrase [Biochemistry](https://www.moldraw.com/templates/biochemistry/)Premium # Carbonic anhydrase template ![Carbonic anhydrase template: In carbonic anhydrase II, OH⁻ on Zn²⁺ (held by His94, His96, His119) attacks CO₂ to give Zn-bound HCO₃⁻, which water displaces; the Zn-bound water (pKa ≈ 7) is deprotonated through His64 to regenerate Zn²⁺–OH⁻.](https://www.moldraw.com/templates/enzyme-carbonic-anhydrase.webp) [Edit in MolDraw](https://www.moldraw.com/)Download with Pro Premium template. Preview and edit it free in MolDraw; downloading and exporting it is part of [MolDraw Pro](https://www.moldraw.com/pricing). In carbonic anhydrase II, OH⁻ on Zn²⁺ (held by His94, His96, His119) attacks CO₂ to give Zn-bound HCO₃⁻, which water displaces; the Zn-bound water (pKa ≈ 7) is deprotonated through His64 to regenerate Zn²⁺–OH⁻. ## Mechanism step by step Zn²⁺-bound hydroxide attacks CO₂; bicarbonate is replaced by water, and His64 shuttles the proton out 1. **OH⁻ attacks CO₂** – Zn²⁺–OH⁻ adds to the carbon of CO₂ bound in a hydrophobic pocket 2. **Water replaces HCO₃⁻** – HCO₃⁻ leaves the zinc; water binds in its place (ligand exchange) 3. **Proton shuttle** – His64 takes H⁺ from Zn²⁺–OH₂ through a chain of waters (rate-limiting) 4. **To the buffer** – His64–H⁺ hands the proton to buffer outside the active site ## Key points - Zn²⁺ lowers the pKa of bound water from about 15.7 to about 7, giving a hydroxide nucleophile at neutral pH. - kcat ≈ 10⁶ s⁻¹ (CA II), among the fastest enzymes; kcat/KM approaches the diffusion limit. - The rate-limiting step is proton transfer: His64 swings between "in" and "out" to pass H⁺ to buffer (the His64Ala mutant is rescued by imidazole buffers). - Sulfonamides such as acetazolamide bind to the zinc and inhibit the enzyme (glaucoma, altitude sickness). Drawn with 65 atoms, 11 arrows, 8 shapes – every one editable in MolDraw. ## Sources - [Berg, Tymoczko, Gatto & Stryer, Biochemistry, 9th ed., 2019, ch. 9](https://openlibrary.org/isbn/9781319114657) Textbook - [Lindskog, Pharmacol. Ther. 1997, 74, 1](https://doi.org/10.1016/s0163-7258(96)00198-2) Review - [Tu, Silverman, Forsman, Jonsson & Lindskog, Biochemistry 1989, 28, 7913](https://doi.org/10.1021/bi00445a054) Original paper ## How to use this template 1. Press **Edit in MolDraw**. The template opens on the canvas of the free MolDraw editor. 2. Change anything: move structures, edit atoms and labels, recolour highlights or delete what you do not need. 3. Add your own structures, arrows and text next to it, or combine several templates on one page. 4. Export the drawing as PNG, SVG or PDF for slides, worksheets, theses and papers. ## Frequently asked questions ### Is the Carbonic anhydrase template free? You can preview the Carbonic anhydrase template here and open and edit it in MolDraw for free. Downloading or exporting it is part of MolDraw Pro, together with the other premium templates. ### Can I edit the Carbonic anhydrase template? Yes. It opens as an ordinary MolDraw drawing, so every structure, arrow, label and colour can be changed, and you can add your own content around it. ### Is the chemistry checked? Every structure is checked with RDKit and every curly arrow passes MolDraw’s electron-flow audit. The sources used are listed on this page. ### Are the biochemical pathways drawn with structures? Yes. 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