Development of novel system to analyze microheterogeneity of alpha_1-acid glycoprotein

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Capillary isoelectric focusing (CIEF) was applied to analyze the glycoforms of alpha1-acid glycoprotein (AGP). AGP was resolved into eight peaks due to the difference in their pI values (pI 3.1-3.5). And the reproducibility of those peaks (CV%) was less than 5% (n=5). The CV% of relative peak area (ratio of each peak area to total peak area) was less than 7.3% for five major peaks, and that of the total peak area was 4.99% (n=5). The calibration line shows good linearity (RSQ>0.99) within the AGP concentration range of 0.35-1.5g/L, which covers the physiological plasma concentration level of AGP.In addition, The role of the branching glycan structure of AGP in the interaction with basic drugs was investigated in terms of enantioselectivity in binding ability. AGP was separated by concanavalin A lectin affinity chromatography into two subfractions, the unretained AGP (UR-AGP) which has no biantennary glycan chain and the retained AGP (R-AGP) which possesses biantennary oligosaccharide chain(s). The unbound concentrations of propranolol (PRO) enantiomers and verapamil (VER) enantiomers in UR-AGP solution and R-AGP solution were determined by high-performance frontal analysis (HPFA) combined with capillary electrophoresis (HPCE/FA). It was found that (S)-PRO is bound to UR-AGP and R-AGP more strongly than (R)-PRO, whereas the reverse applies to VER enantiomers, and that such enantioselectivity is common to these proteins. This suggests that the branching type of glycan chains of AGP does not play significant role in the chiral recognition in binding these basic drugs.