Figure 2.

Schematic view of the most probable formaldehyde-induced modifications in FFPE proteins. Reactive methylol adducts (Δm = 30 Da) are formed as a result of the interaction between formaldehyde and basic amino acid residues, amide groups, or aromatic rings. Unsaturated Schiff base “azomethine” adducts (Δm = 12 Da) are formed as a result of condensation of amino groups with aldehydes or ketones, a reversible reaction with the methylol adduct. Other modification involves formation of acetals. R, organic side chain.