The proton-driven dissociation of oestradiol-receptor dimers as a preparative tool. Isolation of a 32 kDa fragment from porcine uteri and assignment of C-terminal origin by partial sequencing.

Homodimers of the porcine oestradiol receptor dissociated at pH 6.4. The monomers reassociate after neutralization. This property is retained in a 32 kDa receptor fragment generated by co-adsorbed endopeptidases from cytosolic receptor bound to heparin-Sepharose. The fragment was purified by successive gel filtrations in the dimer and monomer states. Precipitations with ethanol and (NH4)2SO4 respectively served as concentrating steps. In all, 10-15 nmol of the homogeneous fragment were recovered from 8 kg batches of porcine uteri with a approximately 10(5)-fold enrichment and in approximately 20% yields. Its oestradiol-binding capacity was identical with that of the intact receptor. The N-terminus was blocked. Two decapeptides from a tryptic digest were sequenced. One of them corresponded to amino acids 353-362 of the human receptor, a sequence fully conserved in all species investigated. The second peptide differed in positions 553, 554 and 557 from the 549-558 sequence of the human protein.