Aqueous two-phase partition studies of glucocorticoid receptors exposed to limited trypsination.

In a previous investigation the properties of glucocorticoid receptors exposed to partial proteolysis by chymotrypsin were studied by aqueous two-phase partitioning (Andreasen, P.A. and Gehring, U. (1981) Eur. J. Biochem. 120, 443-449). This paper describes studies of the properties of cytosolic glucocorticoid receptors submitted to limited trypsination, employing phase partitioning of rat thymocyte cytosol labelled with tritiated triamcinolone acetonide. Trypsin treatment of labelled cytosol at 0 degrees C does not result in any dissociation of steroid from the receptor. The partition properties of the trypsin-treated receptors exposed to receptor-activating conditions are indistinguishable from those of the activated native and chymotrypsin-treated receptors, although the trypsin-treated receptors have lost the affinity for DNA and dextran sulphate. Trypsin treatment of cytosol not exposed to receptor-activating conditions results in a rapid change in the receptor partition coefficients identical to that following chymotrypsin treatment. However, during incubations under conditions at which activation of native and chymotrypsin-treated receptors is very slow, the trypsin-treated receptor is converted to a form with partition properties indistinguishable from those of the activated receptors. During exposure of the cytosol to activating conditions, the time-course of the partition coefficient of the trypsin-treated receptors is only slightly different from that of the native and chymotrypsin-treated receptors, but the trypsin-treated receptors are far less susceptible to the activation inhibitors ATP, Li+ and MoO42-. We conclude that the proteolytic cleavages induced by trypsin in the non-activated receptor do not lead to any immediate changes in the charge and surface properties of the receptor different from those following chymotrypsin treatment, but that the trypsin-treated receptor is not able to maintain a non-activated state and a normal susceptibility to activation inhibitors.