--- title: "Serine protease (chymotrypsin) Template | MolDraw" url: https://www.moldraw.com/templates/enzyme-serine-protease/ description: "Serine protease (chymotrypsin) template: Chymotrypsin cuts a peptide bond in two half-reactions: Ser195 (activated by His57, held by Asp102) attacks the…" 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/) › Serine protease (chymotrypsin) [Biochemistry](https://www.moldraw.com/templates/biochemistry/)Premium # Serine protease (chymotrypsin) template ![Serine protease (chymotrypsin) template: Chymotrypsin cuts a peptide bond in two half-reactions: Ser195 (activated by His57, held by Asp102) attacks the carbonyl to give a tetrahedral intermediate in the oxyanion hole, the amine leaves to give the acyl-enzyme, and water hydrolyses the ester the same way.](https://www.moldraw.com/templates/enzyme-serine-protease.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). Chymotrypsin cuts a peptide bond in two half-reactions: Ser195 (activated by His57, held by Asp102) attacks the carbonyl to give a tetrahedral intermediate in the oxyanion hole, the amine leaves to give the acyl-enzyme, and water hydrolyses the ester the same way. ## Mechanism step by step The catalytic triad Asp102–His57–Ser195: a tetrahedral intermediate, an acyl-enzyme, then hydrolysis by water 1. **Acylation: attack** – His57 takes the Ser195 proton as Ser–O attacks the C=O; Asp102 holds His57–H⁺ in place 2. **Acyl-enzyme** – The O⁻ (in the oxyanion hole) re-forms C=O; the amine N takes H⁺ from His57 and leaves 3. **Deacylation: water attacks** – His57 now activates water; a second tetrahedral intermediate 4. **Release** – C=O re-forms, Ser195 leaves and takes back its proton: free enzyme ## Key points - Ser195 is made a strong nucleophile by His57 (general base); Asp102 orients His57 and stabilises His57–H⁺ (charge-relay system, Blow et al. 1969). - The oxyanion of the tetrahedral intermediate is H-bonded by the backbone NHs of Gly193 and Ser195 (the oxyanion hole), which binds the transition state more tightly than the substrate. - Ping-pong kinetics: the amine leaves before water enters; the covalent acyl-enzyme can be trapped (burst kinetics with p-nitrophenyl acetate). - The S1 pocket sets specificity: large hydrophobic side chains (Phe, Tyr, Trp) for chymotrypsin, Lys/Arg for trypsin (Asp189), small ones for elastase. Drawn with 124 atoms, 17 arrows, 8 shapes – every one editable in MolDraw. ## Sources - [Nelson & Cox, Lehninger Principles of Biochemistry, 8th ed., 2021, ch. 6](https://openlibrary.org/isbn/9781319228002) Textbook - [Berg, Tymoczko, Gatto & Stryer, Biochemistry, 9th ed., 2019, ch. 9](https://openlibrary.org/isbn/9781319114657) Textbook - [Blow, Birktoft & Hartley, Nature 1969, 221, 337](https://doi.org/10.1038/221337a0) 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 Serine protease (chymotrypsin) template free? You can preview the Serine protease (chymotrypsin) 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 Serine protease (chymotrypsin) 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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