Hypochlorous acid oxidizes methionine and tryptophan residues in myoglobin.
After acute myocardial infarction (AMI), infiltrating proinflammatory cells generate two-electron oxidants such as hypochlorous acid (HOCl). Myoglobin (Mb) is present at approximately 0.3 mM in cardiomyocytes and, therefore, represents a significant target for oxidation. Exposure of horse Mb (50 microM) to reagent HOCl (0-500 microM) or activated human neutrophils (4-40x10(6) cells/ml) yielded oxidized Mb (Mb(ox)) as judged by amino acid analysis and peptide mass mapping. HOCl/Mb ratios of 1-5 mol/mol gave Mb(ox) with up to four additional oxygen atoms. Hydrolysis of Mb(ox) followed by amino acid analysis indicated that methionine (Met) and tryptophan (Trp) residues were modified by HOCl. Peptide mass mapping revealed that Met55 was oxidized at a lower HOCl/Mb ratio than Met131 and this preceded Trp7/14 modification (susceptibility Met55>Met131>Trp7>Trp14). Incubation of Mb with activated neutrophils and physiological chloride anion yielded Mb(ox) with a composition similar to that determined with HOCl/Mb ratios <2 mol/mol, with oxidation of Met, but not Trp, detected. These data indicate that Mb undergoes site-specific oxidation depending on the HOCl/protein ratio. As Mb is released from necrotic cardiomyocytes into the vasculature after AMI, HOCl-modified Mb may be a useful surrogate marker to gauge the extent of myocardial inflammation.
Szuchman-Sapir
Andrea J
AJ
Vascular Biology Group, ANZAC Research Institute, Concord Repatriation General Hospital, Concord, NSW 2139, Australia.
Pattison
David I
DI
Ellis
Natasha A
NA
Hawkins
Clare L
CL
Davies
Michael J
MJ
Witting
Paul K
PK
D000595:Amino Acid Sequence; D002700:Chloramines / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D006997:Hypochlorous Acid / Q000494:pharmacology*; D066298:In Vitro Techniques; D008715:Methionine / Q000378:metabolism*; D008969:Molecular Sequence Data; D009211:Myoglobin / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D018375:Neutrophil Activation; D009504:Neutrophils / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D014364:Tryptophan / Q000378:metabolism*
D002700:Chloramines; D009211:Myoglobin; D006997:Hypochlorous Acid; D014364:Tryptophan; D008715:Methionine; C030816:chloramine