title: Deamidation of peptides in aerobic nitric oxide solution by a nitrosative pathway.
abstract: Hydrolytic deamidation of asparagine (Asn) and glutamine (Gln) residues to aspartate (Asp) and glutamate (Glu), respectively, can have significant biological consequences. We hypothesize that a wholly different mechanism of deamidation might occur in the presence of aerobic nitric oxide (NO). Accordingly, we examined the deamidating ability of aerobic NO toward three model peptides, 2,4-dinitrophenyl (DNP)-Pro-Gln-Gly, Lys-Trp-Asp-Asn-Gln, and Ser-Glu-Asn-Tyr-Pro-Ile-Val, incubating them with the NO-generating compound, Et(2)N[N(O)NO]Na (DEA/NO, 30-48 mM), in aerobic, pH 7.4, buffer at 37 degrees C. DNP-Pro-Glu-Gly was detected after 2 h, while Lys-Trp-Asp-Asp-Gln, Lys-Trp-Asp-Asn-Glu, and Ser-Glu-Asp-Tyr-Pro-Ile-Val were detected within 10 min, accumulating in apparent yields of up to approximately 10%. In the latter case, tyrosine nitration was also observed, producing the expected nitrotyrosine residue. DEA/NO solutions preincubated to exhaust the NO before the peptides were added did not induce detectable deamidation. The data demonstrate that aerobic NO exposures can lead to nitrosative deamidation of peptides, a pathway that differs from the established hydrolytic deamidation mechanism in several key respects: the by-products of the former are molecular nitrogen and an acid (HONO) while that of the latter is a base (NH(3)); the nitrosative path can in principle proceed in the absence of water molecules; Asn is much more easily deamidated than Gln in the hydrolytic pathway, while the two amino acid residues were deamidated to a similar extent by exposure to NO in the presence of oxygen.
authors.affiliation: Chemistry Section, Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, MD 21702, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Kong
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Saavedra
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Buzard
authors.forename: Xia
authors.initials: X
authors.lastname: Xu
authors.forename: Brian L
authors.initials: BL
authors.lastname: Hood
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Conrads
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Veenstra
authors.forename: Larry K
authors.initials: LK
authors.lastname: Keefer
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances; D008956:Models, Chemical; D009569:Nitric Oxide / Q000502:physiology*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D004364:Pharmaceutical Preparations
chemical_list: D000596:Amino Acids; D046911:Macromolecular Substances; D010455:Peptides; D004364:Pharmaceutical Preparations; D009569:Nitric Oxide