MODIFICATION OF HISTIDINE-RESIDUES IN BOVINE SERUM-ALBUMIN BY REACTION WITH (E)-2-OCTENAL

Reaction of bovine serum albumin (BSA) with the lipid peroxidation product (E)-2-octenal leads to the generation of (E)-2-octenal-BSA adducts. Amino acid analysis of the modified protein (after reduction with NaBH4) showed that histidine residues were major targets of the reaction and showed the formation of new amino acid derivatives. The same products were detected in acid hydrolysates of poly(L-histidine) and N-(carbobenzoxy)-L-histidine after their reactions with (E)-2-octenal and NaBH4. The reaction of N-(carbobenzoxy)-L-histidine with (E)-2-octenal led to the production of isomeric forms of N-(carbobenzoxy)-1(3)-[1'-(formylmethyl)hexyl]-L-histidine dihydrate. Upon acid hydrolysis, these compounds yielded stoichiometric amounts of histidine. However, after reduction with NaBH4, acid hydrolysis led to a mixture of amino acid derivatives [presumably, isomeric forms of 1(3)-[1'-(hydroxyethyl)hexyl]-L-histidine] that were indistinguishable from those obtained from BSA, poly(L-histidine), and N-(carbobenzoxy)-L-histidine after similar treatment. Although other possibilities are not excluded, it is suggested that the modification of histidine residues in BSA by (E)-2-octenal involves a Michael-type addition of the imidazole nitrogen atom of histidine to the alpha,beta-unsaturated bond of(E)-2-octenal. The reaction of histidine residues with (E)-2-octenal provides the basis for methods by which the contributions of (E)-2-octenal in the modification of proteins can be determined.