V. Baumruk et al., CONFORMATIONAL STUDY OF SEQUENTIAL LYS-BASED AND LEU-BASED POLYMERS AND OLIGOMERS USING VIBRATIONAL AND ELECTRONIC CD-SPECTRA, Biopolymers, 34(8), 1994, pp. 1115-1121
Vibrational CD (VCD) and electronic CD (ECD) spectra of some sequentia
l Lys and Leu based oligo- and polypeptides were studied as a function
of added salt and (for ECD) as a function of concentration in aqueous
solution. For these samples, the VCD spectra can only be measured at
relatively high concentrations under which the well-known salt-induced
transition to a beta-sheet form can be observed for the KL based spec
ies, but only the end-state alpha-helical conformation is obvious for
the LKKL based samples. ECD concentration dependence demonstrates that
, at high concentration with no added or with added salt, LKKL based o
ligomers and polymers give alpha-helical spectra. These data provide e
vidence of aggregation induced secondary structure formation in an exc
eptionally simple peptide system. Similarly, the KL based oligomers an
d polymers give beta-sheet like spectra at high concentration or at hi
gh salt. These systems further provide model systems under ''normal''
aqueous conditions that yield VCD band shapes that correlate to the ma
jor secondary structural types of polypeptides. They are in substantia
l agreement with those spectra obtained on homopolypeptides and on pro
teins, confirming the relative independence of the VCD technique from
side-chain and solvent effects. (C) 1994 John Wiley & Sons, Inc.