COMPARISON OF THE EFFECTS OF OZONE ON THE MODIFICATION OF AMINO-ACID-RESIDUES IN GLUTAMINE-SYNTHETASE AND BOVINE SERUM-ALBUMIN

During exposure to ozone, the methionine and aromatic amino acid resid ues of Escherichia coli glutamine synthetase (GS) and bovine serum alb umin (BSA) are oxidized rapidly in the order Met > Trp > Tyr approxima te to His > Phe. The loss of His is matched by a nearly equivalent for mation of aspartate or of a derivative that is converted to aspartic a cid upon acid hydrolysis. Conversion of His to aspartate was confirmed by showing that the oxidation of E. coli protein in which all His res idues were uniformly labeled with C-14 gave rise to C-14-labeled aspar tic acid in 80% yield and also by the demonstration that His residues in the tripeptides Ala-His-Ala or Ala-Ala-His gave rise to nearly stoi chiometric amounts of aspartic acid whereas oxidation of His-Ala-Ala y ielded only 36% aspartate. The oxidation of BSA and GS led to formatio n, respectively, of 11 and 3.3 eq of carbonyl groups and 0.5 and 0.3 e q of quinoprotein per subunit. Although BSA and GS contain nearly iden tical amounts of each kind of aromatic amino acid residues, oxidation of these residues in BSA was about 1.5-2.0 times faster than in GS ind icating that the susceptibility to oxidation is dependent on the prima ry, secondary, tertiary, and quaternary structure of the protein.