Table 1.

Conserved nitrated tyrosine residues in hemopexin isolates from human, rabbit, and rat plasma

Quantifiable nitration in hemopexin was detected on a few conserved tyrosines as described under “Experimental procedures” and identified using LC-MS/MS of peptides from a trypsin digest of hemopexin from three different species. The predominant nitrotyrosine (Tyrⁿ) identified was a tyrosine in the conserved tryptic peptide YYCFQGNQFLR in human HPX. Using the relative abundance and 3D structural data of heme-hemopexin, the tyrosine most often nitrated in the conserved tryptic peptide YYⁿCFQGNQFLR is from human (Tyr-199), rabbit (Tyr-201), and rat (Tyr-118) hemopexin. This assignment cannot be unequivocally supported by our current MS/MS spectrum analyses (because of the absence of key diagnostic fragments (b-1, or y-10 using collision induced diffusion, or CID on the ion trap) on different species of hemopexin but, as described under “Results,” the structural data allow only this conclusion. These MS/MS data were obtained from the following hemopexin isolates: eight individual human serum samples, three separate pooled rabbit sera samples, and one pooled rat serum. One human hemopexin isolate lacked detectable nitration.

HPX species	NCBI gi no.	Peptide sequence	Tyrn site	Charge (+)	Sequest XCorr	Mascot ions score
Homo sapiens	11321561	198YYnCFQGNQFLR208	199	2	3.068	77.1
Rabbit	130500366	200YYnCFQGNQFLR210	201	2	4.576	67.5
Rat	123036	117YYnCFQGNK124	118	2	2.507	46.9