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synopsisThe 218-nm peak, characteristic of the circular dichroism of randomly coiled poly-aamino acids can be demonstrated in solutions of penta-clysine, a-glycyl-tlysine, as well as poly-clysine. 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-tlysine 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-t 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-clysine 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-tlysine 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-tlysine 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.

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