Structural changes in human serum albumin induced by ingestion of acetylsalicylic acid.

Acetylsalicylic acid (aspirin) acetylates human serum albumin under physiologic conditions in vitro. These investigations were done to determine whether this phenomenon occurs in vivo and to delineate the site(s) of acetylation on the albumin molecule. Albumin was reacted in vitro with aspirin labeled with (14)carbon at the acetyl-1 or the carboxyl carbon. The altered albumin was hydrolyzed with trypsin and peptide mapping performed. Albumin so treated contains a unique peptide, designated "A," and shows diminution of two normal peptides, designated "B" and "C." Peptide "A" is never seen in normal albumin. Amino acid analyses indicate that peptide "A" equals the sum of peptides "B" and "C." Furthermore all three peptides contain lysine but lack arginine. Thus peptide "A" is formed by the acetylation of a lysine residue which is normally susceptible to trypsin and yields peptides "B" and "C." Radioautography of the peptide maps show most of the acetyl-1-(14)C activity in peptide "A." This indicates that one of the lysine residues in this peptide is the preferential site for the transacetylation reaction. Peptide "A," used as a marker for acetylation, is found in albumin from patients who take aspirin but is not demonstrable in albumin from one of these patients while she was taking sodium salicylate. A transacetylation reaction between aspirin and human albumin occurs in vivo and is similar to that observed in vitro.