Deamidation of peptides in aerobic nitric oxide solution by a nitrosative pathway

Hydrolytic deamidation of asparagine (Asn) and glutarnine (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, Et2N[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 LysTrp-Asp-Asp-Gln, Lys-Trp-Asp-Asn-Glu, and Ser-Glu-Asp-Tyr-Pi-o-Ile-Val were detected within 10 min, accumulating in apparent yields of up to similar to 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 (NH3); 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. (c) 2005 Elsevier Inc. All rights reserved.

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