Abstract
The conformational analysis of tyrosyl compounds based on their backbone circular dichroism (CD) spectra was performed. The separation of the backbone CD component of the tyrosyl compounds from natural CD was achieved by fluorescence-detected circular dichroism (FDCD) spectroscopy. The backbone CD spectrum of poly(L-tyrosine) (PLT) in methanol showed two negative extrema at 213 and 222 nm. The solution conformation of PLT was concluded to be the α-helix conformation. The conformational transition of PLT from the α-helix conformation to the β structure was caused by the addition of an aqueous sodium hydroxide solution to the PLT methanol solution. A steep conformational transition was observed within the sodium hydroxide concentration range of 3 × 10−3 to 5 × 10−3 M. The origin of the positive CD band of the tyrosyl compounds near the amide n−π* transition band was experimentally revealed by applying the FDCD method to N-acetyl-L-tyrosinamide, which is a monomer model compound of PLT. The observed CD of N-acetyl-L-tyrosinamide was attributed to the optical rotation coming from the La transition of the phenolic ring on the side chain. N-acetyl-L-tyrosinamide had no backbone CD band in the amide n−π* transition region, whereas the tyrosine dimer, tyrosine trimer, and tyrosine hexamer showed a positive dichroic band derived from the optical activity of their backbone amide chromophores at around 230 nm. The tyrosyl compounds made up of two or more tyrosine residues adopted specific configurations. © 1997 John Wiley & Sons, Inc. Biospect 3: 103–111, 1997
Published Version
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