• Analytical Science and Technology
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• v.25 no.2
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• pp.114-120
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• 2012

For the qualitative analysis of peptides in matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS), O-methylisourea, which is chemically bound to a specific site of an amino acid (e.g. lysine) of peptides and improves the intensities of the modified peptides, is frequently used prior to the MALDI-MS analysis of peptides, where the process is called guanidination. The reaction efficiency of guanidination varies depending on the reaction conditions. We investigated the efficiencies of guanidination of tryptically digested myoglobin using three different reagents (O-methylisourea, S-methylisothiourea, and 2-methyl-2-imidazoline) at $65^{\circ}C$ for 1 h with various pH conditions (pH 4.0, 7.0, and 10.5), where O-methylisourea and pH 10.5 were found to be most effective. The guanidination with O-methylisourea at pH 10.5 were then applied with different reaction conditions such as heating, microwave and ultrasound at various times, where heating for 60 min was found to be most effective. Conclusively, guanidination with O-methylisourea at $65^{\circ}C$ for 1 h at pH 10.5 was found to be the optimized condition.

• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1527-1534
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• 2010

The conventional peptide modification process of guanidination, in which the amino groups of lysine residues are converted to guanidino groups using O-methylisourea to create more basic homoarginine residues, is often used to improve the signal intensity of lysine-containing peptides in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Here, we used three different protease enzymes (trypsin, Lys-C, and Glu-C) to evaluate the effects of guanidination on the MS signals of two enzymatically digested proteins. Horse heart myoglobin and bovine serum albumin were guanidinated either before or after digestion with trypsin, Lys-C, or Glu-C. The resulting peptides were subjected to MALDI-MS, and signal intensities and sequence coverage were systematically evaluated for each digest. Guanidination prior to Glu-C digestion improved sequence coverage for both proteins. For myoglobin, guanidination before enzymatic digestion with trypsin or Lys-C also enhanced sequence coverage, but guanidination after enzymatic digestion enhanced sequence coverage only with Lys-C. For albumin, guanidination either before or after Glu-C digestion increased sequence coverage, whereas pre- or post-digestion guanidination decreased sequence coverage with trypsin and Lys-C. The amino acid composition of a protein appears to be the major factor determining whether guanidination will enhance its MALDI-MS sequence coverage.

• YAKHAK HOEJI
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• v.30 no.5
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• pp.238-244
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• 1986

As one of the starting materials, methylthioacetyl chloride(7) was synthesized in fair yield from mercaptoacetic acid via methyl methylthioacetate(5) prepared by alkylation employing N, N'-dicyclohexyl-O-methylisourea(4). Then 1-$\beta$-D-arabinofuranosylcytosine-5'-methylthioacetate (3) was prepared by esterification of ara-C with obtained methylthioacetyl chloride and tested for inhibitory activity on DNA synthesis in the growing primary hepatocytes and hepatoma strains($H_4$-II-E and HTC cells). In these in vitro cell lines, the inhibitory effect of ara-C-MTA(3) on DNA synthesis was similar to that of its parent ara-C but slightly lower.