Incorporation of two 18O atoms into a peptide during isoaspartyl repair reveals repeated passage through a succinimide intermediate.
To study the mechanism of protein carboxyl methyltransferase-driven repair of age-damaged sites in polypeptides, a model L-isoaspartyl peptide, L-isotetragastrin, was enzymatically repaired to normal L-tetragastrin in the presence of 18O-enriched water. By this design, the enrichment of 18O atoms in the peptide would reflect the number of passages through a hydrolyzable succinimide intermediate during formation of the repaired product. Mass determinations by FAB mass spectrometry revealed repaired peptide with two 18O atoms incorporated, demonstrating that more than a single cycle of methylation and demethylation is necessary to ensure stoichiometric repair.
Department of Biochemistry and Biophysics, Oregon State University, Corvallis 97331.
J A
JA
Lindquist
P N
PN
McFadden
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D013058:Mass Spectrometry; D008745:Methylation; D010103:Oxygen Isotopes; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase; D011496:Protein Methyltransferases / Q000502:physiology*; D013758:Tetragastrin / Q000378:metabolism*
D010103:Oxygen Isotopes; D013758:Tetragastrin; D011496:Protein Methyltransferases; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase