RAMAN-SPECTROSCOPIC STUDY OF CONJUGATES OF BUTYRYLCHOLINESTERASE WITHORGANOPHOSPHATES

Raman spectra of human butyrylcholinesterase (BuChE; E.C. 3.1.1.8) wer e analyzed in the native state and after conjugation with organophosph ates (soman, DFP and paraoxon). The secondary structure of the native BuChE in Tris-HCl buffer (pH 7.5), determined from analysis of the ami de I polypeptide vibration band, indicates 47% alpha-helices, 26% beta -sheets, 16% turns and 12% undefined structure. We obtained the same v alues for paraoxon-phosphorylated BuChE, but 39% helical structure, 31 % beta-sheets, 17% turns and 13% undefined structure for 'aged' DFP-Bu ChE conjugates and 36% helical structure, 34% beta-sheets, 20% turns a nd 10% undefined structure for 'aged' soman-BuChE conjugates, The appr oximate to 10% decrease of alpha-helical structure observed upon phosp horylation by DFP and phosphonylation by soman, probably corresponds t o the 'aging' process, which does not take place in the case of paraox on. Considerable differences have been observed between native, paraox on inhibited and 'aged' BuChE in aromatic ring vibrations, suggesting that the dealkylation of organophosphate conjugates modifies the envir onment or the interactions of aromatic amino-acid residues. In the ali phatic side chains an increase of the number of gauche configurations has been observed in 'aged' DFP-BuChE and soman-BuChE.