Evidence for an intrinsic factor bound to rat alpha1 fetoprotein. Fluorescence investigation

An endogenous chromophore regularly associated with rat alpha, feto- protein was detected by a systematic study of the fluorescence spectra of the protein purified by immunoabsorption.This fluorescent ligand, of low molecular weight, was dissociated from rat alpha l fetoprotein by exhaustive dialysis of the protein at low concentration.A phase partition method with aqueous preparations of rat alpha l fetoprotein allowed extrac- tion of this chromophore into n-butanol and determination of its spectrofluorimetric charac- teristics : an excitation maximum at 305 nm and an emission maximum at 365 nm.We have also shown that this endogenous chromophore competed with estradiol-17P for the same binding sites in rat alpha l fetoprotein.In conclusion, the implication of a specific transport role of this protein for small ligands in fetal development is discussed.of time, showed variations in their estradiol-17P binding properties and also spectral changes related to dialysis times.This paper reports some experiments demonstrating the existence of a fluorescent ligand regularly found associated with rat AFP. Material and methods.Rat AFP preparations.-The rat AFP used was prepared by an immunoabsorption method (Cittanova et al., 1974) which permitted a high degree of purification.Protein concentrations were determined by the method of Lowry (Lowry et al., 1951).