FLUORESCENCE STUDIES OF BETA-ADRENERGIC LIGAND-BINDING TO ALPHA-1-ACID GLYCOPROTEIN WITH 1-ANILINO-8-NAPHTHALENE SULFONATE, ISOPRENALINE, ADRENALINE AND PROPRANOLOL
Johansen, AK; Willassen, NP; Sager, G
The present study shows that ANS (1-anilino-8-naphthalene
sulfonate), propranolol, isoprenaline, adrenaline and dopamine have common binding sites on AAG
(alpha-1-acid glycoprotein). A fluorescence technique was employed to characterize the
interaction between the ligands and AAG at 20-22-degrees. The binding of ANS to AAG caused
increased fluorescence intensity at emission and excitation wavelengths of 400 and 470 nm. In
this situation, propranolol displaced ANS in a concentration-dependent mode with an apparent
dissociation constant of 6.2 +/- 0.01-mu-M, whereas isoprenaline did not reduce the ANS-AAG
fluorescence. However, in the presence of AAG. catecholamines caused a marked increase of
fluorescence at excitation and emission wavelengths of 250 and 325 nm, respectively. These
wavelengths were employed to characterize the binding of isoprenaline, adrenaline and propranolol
to AAG. Two subsets of binding sites were demonstrated. The K(d) values were 0.87 +/- 0.03 and
25.1 +/- 10.7-mu-M for ANS, 0.76 +/- 0.09 and 133 +/- 30.4-mu-M for propranolol, 140 +/- 14 and
2.18 +/- 0.58 mM for isoprenaline, 137 +/- 24 and 14.8 +/- 0.1 mM for adrenaline, respectively.
AAG had identical high affinity binding capacity for these ligands (n almost-equal-to 1).
However, the second class of binding sites showed ligand-dependent binding capacity: n = 1 for
ANS, n almost-equal-to 10 for propranolol, n almost-equal-to 15 for adrenaline, n almost-equal-to
20 for isoprenaline, respectively. ANS, propranolol, dopamine and adrenaline caused
concentration-dependent inhibition of isoprenaline binding to AAG with apparent dissociation
constants of 5.1 +/- 1.8-mu-M, 6.4 +/- 1.1-mu-M, 0.57 +/- 0.13 mM and 1.5 +/- 0.46 mM,
respectively.
Anilino Naphthalenesulfonates; Orosomucoid; Propranolol; 9Y8NXQ24VQ; Isoproterenol; L628TT009W; Ascorbic Acid; PQ6CK8PD0R; Dopamine; VTD58H1Z2X; Epinephrine; YKH834O4BH; Index Medicus; Dose-Response Relationship, Drug; Spectrometry, Fluorescence; Dopamine -- chemistry; Ascorbic Acid -- chemistry; Binding Sites; Epinephrine -- metabolism; Isoproterenol -- metabolism; Propranolol -- chemistry; Epinephrine -- chemistry; Isoproterenol -- chemistry; Orosomucoid -- chemistry; Orosomucoid -- metabolism; Orosomucoid -- isolation & purification; Propranolol -- metabolism