Optical activity of simple peptides. I. Glycine oligopeptides with internal L‐alanyl or ‐L‐glutamyl residues

Abstract

SynopsisOligopeptides containing glycine and one or two Galanyl or tglutamyl residues have been studied by circular dichroism (CD) and optical rotatory dispersion (ORD) in aqueous solution a t pH 1.0, pH 6.0, and pH 10.0 and in aqueous ethanol. Two glycyl residues are required to remove effects of a-carboxyl or amino titration on the optical activity of the internal alanyl or glutamyl residues. The CD spectra of the alanyl and protonated glutamyl residues are similar, having two regions of negative ellipticity with minima around 228 and 195 nm. The CD spectrum of the ionized glutamyl residue has an additional region of positive ellipticity around 215 nm resulting in a spectrum resembling that of poly-a-kglutamic acid (PGA) a t high pH. Another large positive band below 190 nm was observed for glyrglurglyz in water at pH 6 and 10 and for several peptides in aqueous ethanol. Residue ellipticities were approximately additive in every case except for peptides containing internal glutamyl residue at pH 6.0.

Linear oligopeptides. XXVII. Contribution to the circular dichroism of internal peptide chromophores

“…The cd contribution of internal peptide chromophores can be influenced, even in a statistically unordered conformation, by the nature of the residues i~nlnediately adjacent to them (2,20). Thus, the cd patterns of -the various internal peptide chromophores described in this paper represent rigorously only those of the corresponding ho~no-polypeptides in a randomly coiled conforn~ation (usually expressed as mean residue ellipticity), provided solvent and tenlperature are the same.…”

“…The most interesting feature of L-Phe-L-Phe Ii2tel'll(l/ Pellticle C/zroi77ol1/?ore Circrilcrr Di-internal peptide c]lromophore cd resides unclzroism of Srrlfiir-coiztaiiziizg Pepticles doubtedly in the strong positive dichroism The cd curves of L-Met-L-Met and ~-Cys(Me)-ill the 230-217 nm rcgion and below L-Cys(Me) internal peptide chromo~hores are 207 nm (2,20). Conseq~~ently, the cd curve of a illustrated in Fig.…”

“…It is noteworthy that in both cases the dichroism is always negative; however, the spectrum from Gly2-~-Ala?-Gly~ is different from that of Gly?-L-Ala-Gly2 in the sense that in the former the ellipticity above 205 nil1 is clearly less negative, thereby approaching more closely that of curves A , B, and E. This latter finding illustrates well the fact that the intrinsic peptide chromophore cd can be influenced, even in a statistical coil conforn~ation, by the nature of the amino acid residues immediately adjacent to it. In addition, it is of interest that if one subtracts the spectrunl of Gly2-L-Ala-Gly2 from that of Gly2-~-Ala2-Glyl a positive dichroisn~ is apparent in that region around 215-220 nm (2).…”

“…Finally, it is of interest to note that a positive dichroisln around 215 nm is also exhibited .by a n internal L-glutamyl residue (2) and an L-Lys-L-Lys internal peptide chromophoreZ in water, but only in the p H regions where the side chains are ionized.…”