STEROID-PROTEIN INTERACTIONS .20. EFFECT OF CHEMICAL MODIFICATIONS ON PROGESTERONE-BINDING AFFINITY OF ALPHA1-ACID GLYCOPROTEIN

Whereas treatment of α1-acid glycoprotein with dilute acid does not affect the progesterone binding or antigenic activity, both of these properties are eliminated by exposure to dilute alkali. Reduction of the disulfide linkages results in loss of progesterone-binding affinity; reoxidation restores the original activity. Alkylation of the thiol groups of reduced α1-acid glycoprotein by iodoacetic acid and its amide abolishes progesterone binding while the antigenic properties are maintained. Modification of the ε{lunate}-amino groups of lysine leads to virtual disappearance of the steroid-binding affinity; partial removal of the modifying substituent causes partial return of the affinity. The antigenicity is reduced or completely lost, depending on the nature of the reaction. The results show that antigenicity and progesterone-binding affinity are independent properties of the α1-acid glycoprotein molecule. © 1968.