Intrinsic tryptophan fluorescence of membranes of GH 3 pituitary cells: Quenching by thyrotropin-releasing hormone

Abstract

The intrinsic tryptophan fluorescence of membranes prepared from the GH 3 strain of hormone-producing pituitary cells was monitored by spectrofluorometry. Membranes of GH 3 cells have specific receptors which bind thyrotropin-releasing hormone (TRH). When TRH binds to GH 3 membranes there is quenching of tryptophan fluorescence. The kinetics of the change in fluorescence of GH 3 membranes and of TRH binding are similar. In addition, the concentration of TRH required to produce a half-maximum change in fluorescence is 10 nM, and that required for half-maximum binding of TRH to receptors is 11 nM. Inactive TRH analogs which do not bind to TRH receptors likewise do not alter GH 3 membrane fluorescence, and a pituitary cell strain which lacks TRH receptors does not change membrane fluorescence on incubation with TRH. We conclude that the TRH-receptor interaction in GH 3 membranes is associated with a change in membrane conformation that is readily measured by differential spectrofluorometry.