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Solution properties of synthetic polypeptides. I. Light scattering and osmometry of poly-γ-benzyl-L-glutamate in helicogenic solvents

✍ Scribed by Hiroshi Fujita; Akio Teramoto; Koichi Okita; Tsuneko Yamashita; Shoichi Ikeda

Publisher
Wiley (John Wiley & Sons)
Year
1966
Tongue
English
Weight
567 KB
Volume
4
Category
Article
ISSN
0006-3525

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✦ Synopsis

Light-scattering measurements were performed for a number of poly-7-benzyl-Lglutamate (PBLG) samples in dimethylformamide (DMF) and in chloroform-formamide (C-F) a t 25°C. Osmotic pressure data for some of these polypeptide samples in DMF a t 37°C. were also determined. The scattering radii (S2)'/I in the two solvents were roughly proportional to the sample's weighbaverage molecular weight-@,,,.

The lengths per monomeric residue h, calculated from the measured (S2)1/g and M,,, with the assumption of a rigid rod of uniform density, were about 1.2 A. in DMF and about 1.5 A.

in C-F. The measured values for the 2,,,/@% ratio indicated that the samples used were quite polydisperse in molecular weight. If this effect is taken into account, the above values for h must be lowered drastically. In fact, application of Holtzer's procedure, which is capable of yielding h free of polydispersity effects, gave 0.85 A. for h in DMF and 1.16 A. for h in C-F. Since, according to the recent conclusion established by Parry and Elliott, the correct conformation of the PBLG molecule in helicogenic solvents must be the a-helix for which h is 1.5 A., these results imply that the overall shape of the PBLG helix cannot be a rigid rod, in contradictioh to the earlier conclusion of Doty et al.

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