The Goat Blood Binder of Triamcinolone Acetonide Does not Interfere with Glucocorticoid Receptor Purification from Mammary Tissue

Abstract

The high affinity triamcinolone acetonide (TA) binder in goat blood was characterized in the context of our objective to purify glucocorticoid receptor from mammary tissue of the goat. A single class of binding sites was detected exhibiting an apparent equilibrium dissociation constant (Kd) of 1.3 × 10⁻⁷ M, and the binding capacity was found to be 2200 fmol/mg serum protein. Steroid binding specificity studies revealed a unique preference for TA in steroid binding. Unlike the glucocorticoid receptor, the blood TA-binder is thermostable. DEAE-cellulose chromatography resolved the blood binder into two radioactivity peaks. On sucrose gradients, the [³H]TA binder sedimented at 8S. Gel filtration analysis demonstrated a single radioactivity peak exhibiting a Stokes radius of 47 Å. From the hydrodynamic parameters an apparent M_r = 163,500 can be calculated for the blood binder. The blood TA binder displays negligible binding affinity for the steroid ligand of the deoxycorticosterone-deriva-tized affinity resin. These observations demonstrated that the goat blood TA-binding component, and the cytoplasmic glucocorticoid receptor from lactating goat mammary tissue are quite dissimilar entities and, therefore, the blood binder will not interfere with the purification of the glucocorticoid receptor.