Investigation of chiral recognition mechanism on chicken α1-acid glycoprotein using separation system

Chicken α1-acid glycoprotein (α1-AGP) consists of 183 amino acid residues and has only one Trp residue at the 26 position. In this study, the Trp26 residue was modified with 2-nitrophenylsulfenyl chloride and chiral separation of neutral, acidic and basic compounds was examined on chicken α1-AGP and Trp-modified chicken α1-AGP columns. Chiral separation of propranolol, alprenolol and oxprenolol was lost on the Trp-modified chicken α1-AGP column, while chlorpheniramine, ketoprofen and benzoin were still enantioseparated on the Trp-modified chicken α1-AGP column despite of lower enantioselectivity than that on the chicken α1-AGP column. These results suggest that the Trp26 residue could be responsible for chiral recognition of these compounds. Competition studies using N,N-dimethyl-n-octylamine (DMOA) as a competitor indicated that propranolol, alprenolol and oxprenolol competed with DMOA on a single binding site near the Trp26 region and that further bindings of chlorpheniramine, ketoprofen and benzoin occurred at the secondary binding site in a non-competitive fashion with DMOA.