An antibody with dual catalytic activity

Antibodies raised to the bovine serum albumin conjugate of the adduct of acetoxybutadiene with N-(4-carboxybutanoyl)maleimide have been shown to catalyse the Diels-Alder cycloaddition of acetoxybutadiene with N-benzyl- and N-ethyl-maleimide. For one antibody, designated H11, the reaction was selective for 1-acetoxybutadiene; 1-methoxybutadiene and penta-2,4-diene were not substrates. Product inhibition was not observed but the reaction was found to be pH dependent showing a maximum rate at pH 8.5. Analysis of the products of cycloaddition catalysed by H11 indicated that the expected acetoxy adduct was obtained but underwent further reaction catalysed by H11 to afford the corresponding alcohol. This unexpected discovery of a dual catalytic activity associated with an antibody is discussed in the context of hydrolysis reactions catalysed by antibodies.