Aslanian_1995_Biochim.Biophys.Acta_1249_37

Raman spectra of human butyrylcholinesterase (BCHE; E.C. 3.1.1.8) were analyzed in the native state and after conjugation with organophosphates (soman, DFP and paraoxon). The secondary structure of the native BCHE in Tris-HCl buffer (pH 7.5), determined from analysis of the amide I polypeptide vibration band, indicates 47% alpha-helices, 26% beta-sheets, 16% turns and 12% undefined structure. We obtained the same values for paraoxon-phosphorylated BCHE, but 39% helical structure, 31% beta-sheets, 17% turns and 13% undefined structure for 'aged' DFP-BCHE conjugates and 36% helical structure, 34% beta-sheets, 20% turns and 10% undefined structure for 'aged' soman-BCHE conjugates. The approximately 10% decrease of alpha-helical structure observed upon phosphorylation by DFP and phosphonylation by soman, probably corresponds to the 'aging' process, which does not take place in the case of paraoxon. Considerable differences have been observed between native, paraoxon inhibited and 'aged' BCHE in aromatic ring vibrations, suggesting that the dealkylation of organophosphate conjugates modifies the environment or the interactions of aromatic amino-acid residues. In the aliphatic side chains an increase of the number of gauche configurations has been observed in 'aged' DFP-BCHE and soman-BCHE