To investigate the digestion kinetics of Apolipoprotein A-I and B by ID-LC-MS method for accurate quantification of proteins.

Methodological research. The target peptides of ApoA-I and B were determined. The ApoA-I and B from 5 human serum samples on market with levels from 0.90-2.54 g/L and 0.54-1.39 g/L separately, were measured in terms of target peptides by isotope dilution liquid chromatography mass spectrometry method. The releasing amount and rate of peptides were analyzed and plotted according to different time points. The correlation coefficient R² was calculated among peptide releasing amount between samples.

Most peptides reached their peaks within 4 hours. The peptides VQ, DY and VS from Apo A-I, TR and FP from Apo B were released relatively slowly. After getting to their peak stage, the ratio between TEV and SIL-TEV, AK and SIL-AK, VQ and SIL-VQ presented stable state. As for Apo A-I the correlations among peptides are high, from 0.904 to 0.999. Some peptides from Apo B show lower correlations, such as TG-SV with R² 0.543 (3 h).

Peptides from Apo A-I and Apo B present different releasing properties after trypsin digestion. Proper selection of representative peptides and enzymatic conditions can benefit accurate quantification of target proteins.(Chin J Lab Med, 2018, 41: 870-874)

Apolipoprotein A-I; Apolipoproteins B; Kinetics; Chromatography, liquid; Tandem mass spectrometry; Isotope labeling