Modification of Tryptophan Residues on Rhizopus delemar C-Lipase Binding Chlorinated Pesticide by 2-Hydroxy-5-nitrobenzylation.

Abstract

Comparative studies were carried out on the interaction of Rhizopus delemar C-lipase with 1, 1, 1-trichloro-2, 2-bis(4-chlorophenyl)ethane (DDT), 2, 2-bis(4-chlorophenyl)ethane (DIM), dichlorobenzophenone (DCBP) and aldrin by means of 2-hydroxy-5-nitrobenzylation of tryptophan (Trp) residues on the 1 : 1, 2 : 1 and 9 : 1 (7 : 1 with aldrin) pesticide-lipase complexes.2-Hydroxy-5-nitrobenzylation was carried out under three conditions : modification with a water-soluble modification reagent, with the same reagent in the presence of olive oil emulsion and with a fat-soluble modification reagent in the presence of emulsion. The Trp residues involved in ligand-binding were specified in tems of their modification patterns.Modification revealed that the binding of pesticide involves five exposed Trp residues. The modification patterns are distinctly different depending on the sort of pesticide. This is consistent with the previous observation that the binding of the above four pesticides affects the binding properties of the lipase quite differently depending on the sort of pesticide. It is suggested for DDT, DIM and DCBP that the binding of the first pesticide molecule, which governs the ensuing complex formation, involves the same Trp residue. This would indicate the presence of three overlapping binding sites for each of three pesticides. On the other hand, firstly binding two aldrin molecules bind to a region not involving a Trp residue.