Induced CD and interaction of some porphyrin derivatives with α-helical polypeptides in aqueous solutions
✍ Scribed by Shoichi Ikeda; Takashi Nezu; Gotthold Ebert
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1991
- Tongue
- English
- Weight
- 539 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Absorption spectra and induced CD have been measured on aqueous solutions of watersoluble porphyrins with a-helical poly (L-glutamic acid) or a-helical poly (L-lysine) a t different mixing ratios. For the former, porphyrin is porphine-meso-tetra (4-N-methylpyridinium) (TMpyP) , and for the latter, it is porphine-meso-tetra( 4-benzenesulfonate) (TPPS) or porphine-meso-tetra( 4-benzoate) ( T P P C ) . All the solutions of porphyrinpolypeptide systems show hypochromism in the Soret band and induced CD in the Soret region. The CD is characterized by a positive band at a shorter wavelength and a stronger negative band at a longer wavelength. The hypochromicity and the magnitude of molar ellipticities are much larger for the TPPSand TPPC-poly (L-lysine) systems than for the TMpyP-poly (L-glutamic acid) system. Porphyrin ions bind to the a-helix electrostatically, and the two components of the Soret transition of porphyrin are subject to dissymmetric perturbation. TMpyP ions bind to the a-helix at isolated sites, while TPPS ions and TPPC ions are in pairs on the a-helix, that is, two ions bind consecutively and dissymmetrically.
In the TMpyP-poly (L-glutamic acid) system a single CD band is associated with each of the two components of the Soret transition, and these are of opposite sign. In the TPPSand TPPC-poly( L-lysine) systems, a pair of positive and negative CD bands is associated with each of the two components, thus giving apparently a single pair of CD bands with a shoulder, owing to partial overlapping.