Hazime Saitô, I. C. Smith
Sep 1, 1973
Citations
0
Influential Citations
42
Citations
Journal
Archives of biochemistry and biophysics
Abstract
Abstract The helix-coil transition of poly- l -lysine hydrochloride ((Lys)n) in aqueous solution has been studied by 13C Fourier-transform nuclear magnetic resonance spectroscopy. As reference compounds dodeca- l -lysine hydrobromide ((Lys)−12, tri- l -lysine hydrochloride ((Lys)3), and l -lysine hydrochloride (Lys), have been also studied by the same method. It is found that 13C spin-lattice relaxation times t1 of the carbonyl and the side-chain carbons decrease sharply at pD 10.2 which is the midpoint of the transition from the random-coil to the α-helix. Similarly the T1 values of the carbonyl groups of (Lys)−12 decrease at this point in a more moderate way, while no change is observed for those of the side-chain carbons. This is interpreted in terms of the reduced α-helicity involved for (Lys)−12. The variation of 13C chemical shifts with pD for (Lys)n and (Lys)−12 show the same trend:downfield shifts at higher pD. Furthermore, nonterminal and C-terminal residues of (Lys)3 show similar behavior. Thus it is concluded that the 13C chemical shift changes are caused mainly by the pD changes and not by the conformational transition. Conversion from α-helix to β-structure by elevation of temperature at pD 11.2 results in narrowing and downfield shifts of the 13C resonances of (Lys)n.