Abstract: The insulin nitroxide free radical was first prepared and used to study the kinetic changes of the spectral parameters in the process of combination between the insulit:probe and its receptor. The experiments show that before and after combination the conformation of membrane protein, rotational correlation time (τ_c) of insulin molecule and the amplitude (h₀) of ESR spectra of insulin nitroxide free radical have been obviously changed. These changes of parameter of ESR spectrum are related to the endocytose of insulin receptor complexes. The combination could rather be inhibited, when the sulfhydryl group, free amino group or hydroxide group of receptor were blocked.

Key words: ESR spectra, Insulin, Spin labeling