Development of a simple and rapid determination method of <alpha_1> -acid glycoprotein in plasma.

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A cationic fluorescent auramine O (AO) exhibited an intense increase in fluorescence after bindingto human <alpha_1> -acid glycoprotein ( <alpha_1> -AG). The interaction between AO and the protein was studied by fluorescence spectroscopy and by equilibruim dyalysis. AO binds to the protein via a single site with adissociation constant of 24 M. Various basic drugs such as chlorpromazine, imipramine, desipramine, quinidine, propranolol and lidocaine, which are known to bind to the protein, competitively inhibited the AO binding to the protein. The dissociation constants of these basic drugs ontained from such inhibitory experiments were comparable to those obtained with other methods (equilibrium dialysis, quenching of protein intrinsic fluorescence, and the difference spectrophotometric method) and from the literature. It is concluded that AO may be a useful fluorescence probe that binds to a single basic drug binding site on <alpha_1> -AG. In addition, a simple fluorometric method for the determination of <alpha_1> -AG in serum was developed using AO, and the validity of this method was confirmed by comparing it with the conventional radial immunodiffusion method.Treatment of human serum with DEAE-cellulose in acid conditions almost completely removed <alpha_1> -acid glycoprotein ( <alpha_1> -AG) with little change in the concentration of albumin and <beta> -lipoprotein,while treatment with sulphosalicylic acid removed almost all the proteins except <alpha_1> -AG. These results suggest that treatment of serum with sulphosalicylic acid and DEAE cellulose is useful inassessing the contribution of <alpha_1> -AG to the serum binding of basic drugs.