The Synthesis and Circular Dichroism of a Series of Peptides Possessing the Structure (L-Tyrosyl-L-alanyl-L-glutamyl)n.

A series of peptides possessing the structure (L-Tyr-L-Ala-L-Glu)_n, with n = 1, 2, 3, 4, 7, 9, and 13 was synthesized. The oligomers up to n = 4 were prepared by stepwise synthesis using the N-hydroxysuccinimide ester of the tripeptide derivative for the elongation of the chain. The oligomers with n = 7, 9, 13 were prepared by a polycondensation technique, followed by gel filtration. The circular dichroism spectra of the above oligopeptides were measured in the wavelength range 200-330 nm in a solution of 0.15 M sodium chloride -0.02 M sodium phosphate, pH 7.4, conditions at which the high molecular weight polytripeptide (Tyr-Ala-Glu)_n exists in a helical conformation. The circular dichroic spectrum of the high molecular weight polymer exhibits two negative ellipticity bands: an intense band at 220 nm ([θ]_max = 8700) and a weak band at 273 mn ([θ]_max = 360). The tripeptide (n = 1) exhibits a positive ellipticity band at 227 nm ([θ]_max = 4000) and a broad, positive, weak hand at 270 nm ([θ]_max = 115). The other oligopeptides (n = 2 to 13) exhibit positive bands in the 227 n.m region, with ellipticity values that decrease as the degree of polymerization increases. Except for (Tyr-Ala-GIu)₁₃, which has a negative peak centered at 216 nm, circular dichroic spectra of the other oligomers (n = 1 to 9) in the 200-210 nm region resemble that of random coils. In the 260-290 nm region, the circular dichroic curves of the oligopeptides gradually approach the 272 nm band of the polypeptide (Tyr-Ala-Glu)_n, as the degree of polymerization increases. Under physiological conditions, only the (Tyr-Ala-Glu)₁₃ shows an indication of helical content. [ABSTRACT FROM AUTHOR]