title: The binding protein of erythromycin in human serum.
abstract: Erythromycin binding to human serum albumin and to alpha 1-acid glycoprotein was measured under conditions of binding equilibrium. At therapeutical concentrations of erythromycin the binding to albumin is not saturable. The fraction of total erythromycin bound to alpha 1-acid glycoprotein is proportionally related to the protein concentration and is bound to a single class of binding sites with an apparent association constant Ka = 0.16 X 10(6) M-1 (38 degrees). About one mole of erythromycin is bound per mole of alpha 1-acid glycoprotein. The binding affinity can be enhanced and vice versa lowered by increasing the concentrations of NaCl and urea, respectively. The semilogarithmic plot of bound/free ratios vs log concentration of NaCl or urea exhibits linear relationships. Erythromycin binding can be competitively inhibited by mersalyl (Ki = 11-16 microM) but not by other SH-reagents or by neuraminidase treatment. A marked reduction of erythromycin binding to alpha 1-acid glycoprotein is seen with dithiothreitol. alpha 1-acid glycoprotein is the main erythromycin binding protein in human serum.
mesh_terms: D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D004917:Erythromycin / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D009439:Neuraminidase / Q000494:pharmacology; D009961:Orosomucoid / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012709:Serum Albumin / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D009961:Orosomucoid; D012709:Serum Albumin; D013439:Sulfhydryl Reagents; D012965:Sodium Chloride; D004917:Erythromycin; D014508:Urea; D009439:Neuraminidase