Circular dichroism and proton magnetic resonance studies of random chain poly-L-lysine

✍ Scribed by Richard M. Epand; Graham E. Wheeler; Mario A. Moscarello

• Publisher: Wiley (John Wiley & Sons)
• Year: 1974
• Tongue: English
• Weight: 427 KB
• Volume: 13
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1974.360130211

✦ Synopsis

Abstract

The 218‐nm peak, characteristic of the circular dichroism of randomly coiled poly‐α‐amino acids can be demonstrated in solutions of penta‐L‐lysine, α‐glycyl‐L‐lysine, as well as poly‐L‐lysine. The thermal stability of the particular state that gives rise to this 218‐nm band in the CD is similar for all three peptides. These results eliminate the possibility that poly‐L‐lysine forms a structure with long‐range order in acidic aqueous solution since the stability of such a structure would be expected to be greater for a higher molecular weight polymer than for a pentamer. The intrinsic viscosity of poly‐L‐lysine of molecular weight 180,000 varies only slightly between 25 and 60°C. The proton magnetic resonance spectra of poly‐L‐lysine and penta‐L‐lysine are indistinguishable on the basis of the chemical shift of all resonances, their line widths, and the exchange rates of the NH protons. This demonstrates that poly‐L‐lysine does not possess a cooperatively formed ordered structure in acidic solutions.

A weak band at 238 nm is observed in the circular dichroism of poly‐L‐lysine and other peptides. It is suggested that the effects of change in temperature, salt concentration, or polymer on both the magnitude and position of the 238‐nm band may be explained if it is assumed that it is a shoulder of a lower wavelength peak.