Abstract
During exposure to ozone, the methionine and aromatic amino acid residues of Escherichia coli glutamine synthetase (GS) and bovine serum albumin (BSA) are oxidized rapidly in the order Met > Trp > Tyr approximately His > Phe. The loss of His is matched by a nearly equivalent formation of aspartate or of a derivative that is converted to aspartic acid upon acid hydrolysis. Conversion of His to aspartate was confirmed by showing that the oxidation of E. coli protein in which all His residues were uniformly labeled with 14C gave rise to 14C-labeled aspartic 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 stoichiometric amounts of aspartic acid whereas oxidation of His-Ala-Ala yielded only 36% aspartate. The oxidation of BSA and GS led to formation, respectively, of 11 and 3.3 eq of carbonyl groups and 0.5 and 0.3 eq of quinoprotein per subunit. Although BSA and GS contain nearly identical 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 indicating that the susceptibility to oxidation is dependent on the primary, secondary, tertiary, and quaternary structure of the protein.
Highlights
Because of its pronounced cytotoxicity, recent studies have focused on the fact that ozone can give rise to a number of other reactive oxygen species including O H, H2O2, O2., RCOO1⁄7, O3., and singlet oxygen (9 –15)
These two proteins are similar with respect to subunit size (50 versus 67 kDa), they contain nearly equal numbers of Trp, Tyr, His, and Phe residues per subunit, and x-ray crystallographic data are available for glutamine synthetase (GS) [24] and human serum albumin [25], which is highly homologous to bovine serum albumin (BSA)
Secondary, tertiary, and quaternary structures of the proteins is strengthened by the results presented here, because the subunits of BSA and GS are of comparable size and contain nearly equal numbers of each of the aromatic amino acids
Summary
Vol 271, No 8, Issue of February 23, pp. 4177–4182, 1996 Printed in U.S.A. Comparison of the Effects of Ozone on the Modification of Amino Acid Residues in Glutamine Synthetase and Bovine Serum Albumin*. We compare the ability of ozone to oxidize amino acid residues in Escherichia coli glutamine synthetase (GS) and bovine serum albumin (BSA). These two proteins are similar with respect to subunit size (50 versus 67 kDa), they contain nearly equal numbers of Trp, Tyr, His, and Phe residues per subunit, and x-ray crystallographic data are available for GS [24] and human serum albumin [25], which is highly homologous to BSA. We investigated the ozone-mediated oxidation of a series of tripeptides, each of which contained two alanine residues and one histidine residue that was present in either the N-terminal, middle, or C-terminal position
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