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Secondary structure of peptides. 18. 15N-nmr and 13C-nmr CP/MAS investigation of the primary and secondary structure of (Ala/Val) copolypeptides

✍ Scribed by Hans R. Kricheldorf; Detlef Müller; William E. Hull

Publisher
Wiley (John Wiley & Sons)
Year
1985
Tongue
English
Weight
859 KB
Volume
24
Category
Article
ISSN
0006-3525

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✦ Synopsis

Rheinstetten 4, Federal Republic of Germany

Synopsis

Various copolypeptides were prepared by benzylamine or tertiary amine-initiated copolymerizations of alanine-N-carboxyanhydride (Ah-NCA) and valine-N-carboxyanhydride (Val-NCA). The number-average molecular weights of these copolypeptides were determined by 'H-nmr spectroscopic end-group analyses and viscosity measurements. The sequences were characterized by ' W n m r spectra in solution, and the average lengths of the homogeneous blocks were determined from the signal intensities. The 50.3and 75.4-MHz W n m r CP/MAS spectra of the solid copolypeptides are not sensitive to sequence effects, but allow qualitative and quantitative analyses of the secondary structures. In contrast to other methods, the Y -n m r spectra allow determination of the extent to which individual amino acids are incorporated into P-sheet or a-helix phases. Depending on primary structure and molecular weight, the secondary structure of (Ala/Val) copolypeptides may vary significantly. Both monomer units may be predominantly helical or predominantly P-sheet structure, or the Val units may prefer the P-sheet structure with most Ala-units forming a-helices. However, these secondary structures are more or less thermodynamically unstable and revert to the stable conformations on reprecipitation from trifluoroacetic acid/water.

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