title: Characterization of [peptide+(Ag)n]+ complexes using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.
abstract: Silver ion complexes of peptides [M + (Ag)(n) ](+) , M = angiotensin I or substance P where n = 1-8 and 17-23 for angiotensin I and n = 1-5 for substance P, are identified and characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The Ag(+) coordination number exceeds the number of available amino acid residues in angiotensin I whereas the number of observed complexes in substance P is less than the number of amino acid residues in it. The larger coordination number of angiotensin I with Ag(+) indicates the simultaneous binding of several Ag(+) ions to the amino acid residue present in it. The lower number of observed complexes in substance P suggests the binding of two or more residues to one Ag(+) ion. The presence of trifluoroacetic acid in the peptide samples reduces the Ag(+) coordination ability in both the peptides which indicates that the basic residues in it are already protonated and do not participate in the Ag(+) -binding process. The Ag(+) ion also forms a complex with the α-cyano-4-hydroxycinnamic acid (CHCA) matrix and is observed in the MALDI mass spectra and the formation of [CHCA + Ag](+) , [CHCA + AgNO(3) ](+) and [(CHCA)(2)  + Ag](+) ions is due to the high binding affinity of Ag(+) to the CN group of CHCA.
authors.affiliation: Applied Spectroscopy Division, Bhabha Atomic Research Centre, Mumbai 400 085, India. jsekhar@barc.gov.in
authors.forename: T
authors.initials: T
authors.lastname: Jayasekharan
authors.forename: N K
authors.initials: NK
authors.lastname: Sahoo
mesh_terms: D000803:Angiotensin I / Q000737:chemistry / Q000378:metabolism; D003373:Coumaric Acids / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008667:Metalloproteins / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D018030:Silver Compounds / Q000737:chemistry* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013373:Substance P / Q000737:chemistry / Q000378:metabolism; D014269:Trifluoroacetic Acid / Q000737:chemistry
chemical_list: D003373:Coumaric Acids; D008667:Metalloproteins; D010455:Peptides; D018030:Silver Compounds; C007175:alpha-cyano-4-hydroxycinnamate; D013373:Substance P; D000803:Angiotensin I; D014269:Trifluoroacetic Acid