Binding and mobility of the cell surface receptors for 3,3',5-triiodo-L-thyronine.

A fluorescent derivative of the thyroid hormone 3,3'-triiodo-L-thyronine binds to cultured mouse fibroblasts; such binding is saturable. Video intensification fluorescence microscopy indicates that binding occurs at the plasma membrane. Diffusion coefficients, obtained by fluorescence photobleaching recovery, are consistent with binding to a protein receptor on the cell surface.