Improved peptide detection with matrix-assisted laser desorption/ionization mass spectrometry by trimethylation of amino groups.
Trimethyl alpha-amino derivatives of peptides (penta to deca) with a permanent positive charge on their alpha-amino groups were prepared by in vacuo reaction with iodomethane and subjected to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Compared to the unmodified peptide, the signal intensity of the trimethyl alpha-amino derivative in MALDI-MS is increased by at least an order of magnitude. Similarly, an octapeptide with a trimethylated epsilon-amino group derived from the solitary lysine residue of the B-chain of insulin also shows the same relative increase in signal intensity. Another advantage of the in vacuo methylation procedure is that trimethylation of a peptide amino group can be carried out readily with a combination of isotopes (13)CH(3)I and (12)CH(3)I or CD(3)I and CH(3)I, yielding a doublet signal either 3 or 9 units apart, respectively. The presence or absence of such a doublet signal can be used as a criterion to discriminate between peptide and non-peptide signals in the mass spectrum.
Department of Chemistry, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
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Stewart
V T
VT
Pham
C T
CT
Choma
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H
Kaplan
D000588:Amines / Q000737:chemistry*; D000818:Animals; D002417:Cattle; D006868:Hydrolysis; D007328:Insulin / Q000032:analysis; D008745:Methylation; D010084:Oxidation-Reduction; D012997:Solvents; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin
D000588:Amines; D007328:Insulin; D012997:Solvents; D014357:Trypsin