Revisit of MALDI for small proteins.
Matrix-assisted laser desorption/ionization (MALDI) was used for several small proteins (such as insulin) and for peptides. It was found that the detection efficiencies of MALDI for the insulin B chain and the insulin A chain are drastically different. Similar phenomena were also observed for various types of peptides. The positive-ion signal of MALDI in detecting proteins or peptides was found to be greatly enhanced by the presence of a basic amino acid in their chains. The experimental results indicate that this enhancement may arise from proton transfer in solution by an acid-base reaction between the protein/peptide and matrix molecule. This pre-protonated mechanism provides a low energy barrier for the ionization of peptides in a MALDI process, and greatly reduces the energy threshold of MALDI. Matrix effects on the ionization mechanism are discussed.
Oak Ridge National Laboratory, Health Sciences Research Division, Tennessee 37831-6378, USA.
Y F
YF
Zhu
K L
KL
Lee
K
K
Tang
S L
SL
Allman
N I
NI
Taranenko
C H
CH
Chen
D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D006639:Histidine / Q000737:chemistry; D007328:Insulin / Q000032:analysis; D008239:Lysine / Q000737:chemistry; D008969:Molecular Sequence Data; D011506:Proteins / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet
D007328:Insulin; D011506:Proteins; D006639:Histidine; D001120:Arginine; D008239:Lysine