title: Interaction between human serum albumin and alpha 1-acid glycoprotein in the binding of lidocaine to purified protein fractions and sera.
abstract: The authors have determined the binding parameters for [14C] lidocaine to several preparations of purified human serum alpha 1-acid glycoprotein (AAG) and human serum albumin (HSA). The authors find that the average Kd for the three different purified AAG preparations was 15.2 +/- 0.5 microM, with an average of 0.567 +/- 0.009 binding sites (N) per AAG molecule, when the concentration of AAG was determined by a standard colorimetric protein assay. The number of binding sites per AAG increased to 0.99 +/- 0.06 when the concentration of AAG was determined immunologically. On the other hand, delipidized AAG had a Kd of 28.0 microM, with an N of 1.72 based on the immunological assay. Various preparations of HSA had Kd/N values ranging from 4.3 to 17.3 mM. The number of binding sites per HSA molecule could not be determined because the maximum concentration of lidocaine that can be used is 10 mM, which is only approximately equal to the Kd. The Kd to HSA was so low and the capacity so high that, at therapeutic concentrations, the binding was in the linear range. Solutions containing both purified AAG and HSA had Kd values of 30.2 +/- 1.8 microM, with 2.01 +/- 0.04 binding sites per AAG molecule. With HSA and delipidized AAG, the Kd was 60 microM, with 3.16 sites per delipidized AAG molecule. This increase in the binding parameters appeared to be due to a direct interaction between the two proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D001665:Binding Sites; D001798:Blood Proteins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008012:Lidocaine / Q000378:metabolism*; D008433:Mathematics; D009961:Orosomucoid / Q000378:metabolism*; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism*
chemical_list: D001798:Blood Proteins; D009961:Orosomucoid; D012709:Serum Albumin; D008012:Lidocaine