Fig. 1.

Scheme showing the two potential pathways by which BP covalently bound to protein. Pathway 1: direct binding of BP (1) with epsilon amino groups of lysine residues by opening of the β-lactam ring. Pathway 2: rearrangement of BP (1) to PA (2) followed by nucleophilic attack on lysine residues to form diastereoisomeric adducts (3) and (4).