title: Binding of the chymotrypsin substrate, tryptophan methyl ester, by rat alpha-fetoprotein.
abstract: We studied how tryptophan methyl ester and related compounds inhibit binding of estrone to rat alpha-fetoprotein and find that: (a) like chymotrypsin, alpha-fetoprotein binds tryptophan esters with higher affinity than tryptophan or its amides; (b) the affinity of alpha-fetoprotein for tryptophan methyl ester is 3.7 . 10(-4) M, which is close to the affinity of chymotrypsin (10(-4) M); (c) alpha-fetoprotein binding of tryptophan methyl ester is stereoselective and pH dependent. All of these observations suggest that there is a specific interaction between alpha-fetoprotein and the chymotrypsin substrate, tryptophan methyl ester, and that rat alpha-fetoprotein contains a site with some structural similarities to the catalytic site in chymotrypsin. Since we also find that tryptophan methyl ester is a competitive inhibitor of estrone binding to alpha-fetoprotein, it is possible that the protease substrate binding site on alpha-fetoprotein is spatially close to the estrone binding site.
mesh_terms: D000818:Animals; D002918:Chymotrypsin / Q000378:metabolism; D004970:Estrone / Q000378:metabolism; D007700:Kinetics; D011485:Protein Binding; D051381:Rats; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000378:metabolism; D000509:alpha-Fetoproteins / Q000378:metabolism*
chemical_list: D000509:alpha-Fetoproteins; D004970:Estrone; C028129:tryptophan methyl ester; D014364:Tryptophan; D002918:Chymotrypsin