CONFORMATIONAL STUDIES ON SYNTHETIC POLY-α-AMINO ACIDS: THE HELICAL SENSE OF POLY-L-TRYPTOPHAN: OPTICAL ROTATORY DISPERSION STUDIES

Abstract

The synthesis of high n~olecular weight (100 000 to 200 000) polymers and copolymers of L-tryptophan and y-benzyl-L-glutamate is reported. The optical rotatory dispersion (0.r.d.) of these polypeptides is recorded in the wavelength range 540-320 mp and the bo values of the Moffitt equation, using X O = 212 mp, are listed. Poly-L-tryptophan has a bo value of f 570 in dimethylforman~ide (DMF). A linear relationship exists between this value, bo values of copolymers of various ratios of L-tryptophan and y-benzyl-L-glutamate, and the value of -670 found for poly-r-benzyl-~-glutamate. T h e 0.r.d. curve of a poly-L-tryptophan film, in the 330-200 mp wavelength range, reveals two positive Cotton effects in the 370-290 m p region and a large negative Cotton effect a t 233 mp. Thus, despite the positive bo value, these data prove that poly-L-tryptophan, in DMF, has the right-handed helical conformation. Hypochromicity was found for the tryptophanyl residue in the helical polypeptide. T h e rotatory contribution of chromophores, such as tryptophan or coenzymes, when bound asymmetrically to a protein, can be very significant, and caution is advised in the interpretation of such 0.r.d. curves.Optical rotatory dispersion (0.r.d.) measurements have become extensively used to determine the conformation of proteins (1, 2, 3). The anomalous rotatory dispersion curves for many synthetic poly-a-amino acids and proteins in the helical conforn~ation have been adequately interpreted by the Moffitt equation (4, 5) [nz1]x = aoXo2/(X" Xo2) + bOXo4/(X2 -kg2)?. Although it is acknowledged that this treatment of 0.r.d. data is of a highly empirical nature, the constant bo in this equation has been successfully used as a measure of the helical content in polypeptides and proteins. The bo value of approximately -630 to -670 (XO = 212 mp) has been found for the 100% right-handed helical conformation (5, 6), while the random coil form has a bo value of zero (6). The sign of the bo has been taken to indicate the sense of helix, and has been corroborated by X-ray studies (7). Estimates of helical content derived from 0.r.d. data (8, 9) agree remarkably well with X-ray data for myoglobin (10). More recently a modified Drude equation (11) has been proposed to estimate helical contents in polypeptides based on 0.r.d. studies penetrating further into the ultraviolet region. However, this treatment is theoretically inadequate, as a new Cotton effect has since been discovered (Holzwarth and Doty (12) have shown that the 233 mp Cotton effect is a composite of two such bands and that two circular dichroism bands are responsible for this Cotton effect, one caused by a n -+ n* transition and the other caused by a n -+ n* transition), which liltewise places

Fish sarcoplasmic proteins as a high value marine material for wound dressing applications

“…Until 229 nm, the FSP-M shows linear response, and then it becomes negative, with a peak between 254 and 231 nm, and a minimum negative at ≈ 241 nm. Fasman et al described a peak at 276 nm in the CD spectrum of L-Tryptophan, explaining that it represents a superposition of the ␣-helix bands and of the strong aromatic chromophore bands which are present in the near UV region [40]. This argument is in agreement with the applied Reed's reference, which describes a 100% ␣-helix structure.…”

Aggregate formation and release behaviour of hydrophobic drugs with graft copolypeptide‐containing tryptophan

“…The b 0 value in DMF calculated by Moffitt's equation was +495. Fasman et al performed the conformation analysis of poly(Trp) with a molecular weight 123 000 g mol −1 , and reported that the poly(Trp) forms a α‐helix structure with b 0 value of +570 30–32. Although the poly(Trp) used in this study can form α‐helix structures, the ordered structure seems to have not been formed at its molecular terminal since the degree of polymerization was not sufficiently high.…”

Aggregate formation and release behaviour of model substances with block co-polypeptide containing tryptophan

“…The b 0 value in DMF calculated by Moffitt's equation was C495. Fasman et al performed the conformation analysis of poly (Trp) with a molecular weight 123,000 g/mol, and reported that the poly(Trp) forms a a-helix structure with b 0 value of C570 [29][30][31]. Although the poly(Trp) used in this study can form a-helix structure, the ordered structure seems to have not been formed at its molecular terminal since the degree of polymerisation is not sufficiently high.…”