8 ICPL (isotope-coded protein label), 9 and iTRAQ (isobaric tag for relative and absolute quantification). 10 These methods require not only a specific antibody, but also an amino acid-specific labeling reagents. New protein quantification methods that do 2014 © The Japan Society for Analytical Chemistry † To whom correspondence should be addressed. E-mail: nfuruta@chem.chuo-u.ac.jp Y. S. present address: Faculty of Life and Environmental Science, Department of Regional Environmental Science, Shimane University, 1060 Nishikawatsu-cho, Shimane, Japan.
Quantification of Proteins by Measuring the Sulfur Content of Their Constituent Peptides by Means of Nano HPLC-ICPMSYoshinari SUZUKI, Ayumi NOBUSAWA, and Naoki FURUTA † Faculty of Science and Engineering, Department of Applied Chemistry, Chuo University, Bunkyo, Japan The sulfur (S) concentrations of three peptides were determined by using nano HPLC-ICPMS under a flow of O2 in an octapole reaction cell, and the determined values showed a good agreement with theoretical values. This method was then applied to trypsin-digested peptides from human albumin for protein quantification. Assigning of the number of S atoms in each peptide/peak and the tryptic digestion efficiency were important for protein quantification. The number of S atoms in each peptide/peak was assigned by using verification scores that gave the lowest standard deviation of the peptide S concentration and the highest S recovery. The peptide concentrations were calculated as the ratio of the S concentration/the number of S atoms in the peptide/peak. The tryptic digestion efficiency was calculated as the sum of the S concentration in the mono-peptides divided by the total S concentration in a native polyacrylamide gel electrophoresis (PAGE) band before tryptic digestion. Our result indicates that a protein can be quantified through peptide quantification, after taking into account the tryptic digestion efficiency, via S quantification using ICPMS.