Rat alpha-fetoprotein contains a site that both binds serine enzyme inhibitors and substrates and regulates estrogen binding. We report that mM concentrations of the histidine selective reagent, diethylpyrocarbonate, inhibit estrogen binding to rat alpha-fetoprotein and that this inhibition is reversed by hydroxylamine. We suggest that rat alpha-fetoprotein contains one or more histidine residues that regulate estrogen binding. We also find that either estrone or the chymotrypsin substrate, acetyl-tryptophan methyl ester, protects rat alpha-fetoprotein from diethyl-pyrocarbonate-mediated inhibition of estrogen binding. We infer that the protease substrate and estrogen binding sites contain histidine residue(s) essential for estrogen binding by alpha-fetoprotein.
Read full abstract