--- title: "Class I aldolase (Schiff base) Template | MolDraw" url: https://www.moldraw.com/templates/enzyme-aldolase-schiff-base/ description: "Class I aldolase (Schiff base) template: Fructose 1,6-bisphosphate (open chain) forms a protonated Schiff base with Lys229; Asp33 removes the C4–OH proton…" 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/) › Class I aldolase (Schiff base) [Biochemistry](https://www.moldraw.com/templates/biochemistry/)Premium # Class I aldolase (Schiff base) template ![Class I aldolase (Schiff base) template: Fructose 1,6-bisphosphate (open chain) forms a protonated Schiff base with Lys229; Asp33 removes the C4–OH proton, the C3–C4 bond breaks with the iminium as electron sink to release glyceraldehyde 3-phosphate, and the enamine is protonated and hydrolysed to dihydroxyacetone phosphate.](https://www.moldraw.com/templates/enzyme-aldolase-schiff-base.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). Fructose 1,6-bisphosphate (open chain) forms a protonated Schiff base with Lys229; Asp33 removes the C4–OH proton, the C3–C4 bond breaks with the iminium as electron sink to release glyceraldehyde 3-phosphate, and the enamine is protonated and hydrolysed to dihydroxyacetone phosphate. ## Mechanism step by step Lys229 forms an iminium ion with fructose 1,6-bisphosphate; a retro-aldol cleavage of C3–C4 releases GAP 1. **Lys229 adds to C2** – The ε-amino group attacks the ketone: a carbinolamine (zwitterion) 2. **Iminium ion** – Proton transfers and loss of water: the protonated Schiff base (arrows not shown) 3. **Retro-aldol cleavage** – Asp33 takes the C4–OH proton; C3–C4 breaks and the iminium takes the electrons 4. **Enamine protonation** – C3 takes a proton: the iminium ion of DHAP 5. **Hydrolysis (summarised)** – Water adds to C=N⁺ and Lys229 leaves: DHAP and free enzyme ## Key points - The protonated Schiff base (iminium) is a better electron sink than C=O, so it stabilises the C3 carbanion/enamine (Horecker: NaBH₄ traps it on Lys). - Class II aldolases (bacteria, fungi) use Zn²⁺ instead of a Schiff base to polarise the carbonyl. - ΔG°′ = +23.8 kJ/mol, yet in cells ΔG ≈ 0 because the products are removed and kept at low concentration. - In gluconeogenesis the same enzyme runs the aldol forward: DHAP + GAP → fructose 1,6-bisphosphate. Drawn with 235 atoms, 15 arrows, 8 shapes – every one editable in MolDraw. ## Sources - [Nelson & Cox, Lehninger Principles of Biochemistry, 8th ed., 2021, ch. 14](https://openlibrary.org/isbn/9781319228002) Textbook - [Berg, Tymoczko, Gatto & Stryer, Biochemistry, 9th ed., 2019, ch. 16](https://openlibrary.org/isbn/9781319114657) Textbook - [Grazi, Rowley, Cheng, Tchola & Horecker, Biochem. Biophys. Res. Commun. 1962, 9, 38](https://doi.org/10.1016/0006-291x(62)90083-9) 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 Class I aldolase (Schiff base) template free? You can preview the Class I aldolase (Schiff base) 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 Class I aldolase (Schiff base) 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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