C. Dass et P. Mahalakshmi, AMINO-ACID-SEQUENCE DETERMINATION OF PHOSPHOENKEPHALINS USING LIQUID SECONDARY IONIZATION MASS-SPECTROMETRY, Rapid communications in mass spectrometry, 9(12), 1995, pp. 1148-1154
Liquid secondary ionization mass spectrometry (LSIMS) operating in the
positive- and negative-ion modes was used to study fragmentation prof
iles and to obtain the amino acid sequences of a set of seven phosphoe
nkephalin peptides. The use of glycerol as the liquid matrix led to in
crease in fragmentation of phosphopeptides, The prominent amino acid s
equence-determining ions in the positive-ion mode are y-type C-termina
l ions; the N-terminal sequence-specific ions are observed sporadicall
y. The most dominant ions in those mass spectra, however, are the immo
nium ions and a few low-mass side-chain cleavage products. The mass sp
ectra in the negative-ion mode are more information-rich, and provide
data complementary to that from the positive-ion mode. The phosphate g
roup marker ions, m/z79 (PO3-) and 97 (H2PO4-), are prominent and both
N- and C-termini sequence ions are formed with equal facility in this
mode of analysis. Both positive- and negative-ion mass spectral data
are useful in determining the amino acid sequence of all of the seven
phosphoenkephalins. Thus, LSIMS alone can be a viable option to the ta
ndem mass spectrometry approach when sufficient quantities (>50 nmol)
of phosphopeptides are available.