The Reversible Reaction of Protein Amino Groups

1. The reaction of exo-ci8-3,6-endoxo-A4-tetrahydrophthalic anhydride with amino groups ofmodel compounds and lysozyme is described. 2. Reaction with the e-amino group of Na-acetyl-L-lysine amide gives rise to two diastereoisomeric products; at acidpH the free amino group is liberated with anchimeric assistance by the neighbouring protonated carboxyl group with a half-time of 4-5h at pH 3.0 and 25°C. 3. The amino groups of lysozyme can be completely blocked, with total loss of enzymic activity. Dialysis at pH 3.0 results in complete recovery of the native primary and tertiary structure of lysozyme and complete return of catalytic activity. 4. The specificity of reaction of this and other anhydrides with amino groups in proteins is discussed.