title: Fluorescence energy transfer studies on lima bean lectin. Distance between the subunit hydrophobic binding site and the thiol group essential for carbohydrate binding.
abstract: Measurements of the efficiency of singlet-singlet energy transfer were used to determine the distance between the hydrophobic binding site and the thiol group required for carbohydrate-binding activity of lima bean lectin. 1-Anilino-8-naphthalenesulfonate, bound to the hydrophobic binding site by noncovalent interactions, was used as the donor. Two different nonfluorescent probes were used as the acceptors: a mercurial, 2-chloromercuri-4-nitrophenol, and a maleimide, 4-dimethylaminophenylazophenyl-4'-maleimide. Acceptor was covalently attached to the thiol group at the putative carbohydrate binding site. The efficiency of energy transfer in both the 1-anilino-8-naphthalenesulfonate/2-chloromercuri-4-nitrophenol and and 1-anilino-8-naphthalenesulfonate/4-dimethylaminophenylazophenyl-4' -maleimide donor-acceptor systems indicated an apparent distance of 28 A between the two sites, assuming that the transition dipole of the donor is not correlated with respect to that of the acceptor and that each donor is quenched by a single acceptor. Using an alternate model wherein each donor is equally quenched by two acceptors on adjacent subunits, an apparent distance of 33.4 A was calculated. The fact that two donor-acceptor pairs with different Förster's critical distance parameters yielded the same distance between the sites is consistent with our assumption of uncorrelated donor-acceptor transition dipoles.
mesh_terms: D001665:Binding Sites; D004735:Energy Transfer; D005456:Fluorescent Dyes; D006384:Hemagglutination; D006801:Humans; D037102:Lectins / Q000302:isolation & purification; D046911:Macromolecular Substances; D008433:Mathematics; D037121:Plant Lectins; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D037102:Lectins; D046911:Macromolecular Substances; D037121:Plant Lectins; C031887:lima bean lectin