Pea seedling extracts catalyze protein amine binding and protein cross-linking .2. Contribution of diamine oxidase to these reactions

The activity of a purified pea diamine oxidase (DAO) was compared to that of a pea seedling enzymatic extract (PPE). It has been shown that DAO is able to catalyze as PPE the binding of amine to proteins as well as protein cross-linking reactions, but only if diamines and Cu2+ ions are both available in the medium. We proposed a mechanism in two steps for this reaction: first, an enzymatic step which induces the formation of an aldehyde resulting from the enzymatic oxidation of the diamine by DAO and, second, a chemical step catalyzed by Cu2+ which corresponds to the addition of nucleophilic amino acid side chain with the carbonyl group of the aldehyde. This last chemical reaction may lead in a first stage to the amine binding or in a second stage to protein cross-linking.