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Hemoprotein Models Based on a Covalent Helix–Heme–Helix Sandwich: 2. Structural Characterization of Co III Mimochrome I δ and δ Isomers
Author(s) -
D'Auria Gabriella,
Maglio Ornella,
Nastri Flavia,
Lombardi Angela,
Mazzeo Marco,
Morelli Giancarlo,
Paolillo Livio,
Pedone Carlo,
Pavone Vincenzo
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970030306
Subject(s) - diastereomer , chemistry , hemeprotein , heme , covalent bond , helix (gastropod) , crystallography , spectroscopy , stereochemistry , nuclear magnetic resonance spectroscopy , proton nmr , organic chemistry , ecology , physics , quantum mechanics , snail , biology , enzyme
Fe III mimochrome I is the prototype of a new class of hemoprotein models characterized by a covalent helix–heme–helix sandwich. It contains deuterohemin bound through two propionyl groups to two identical N ‐ and C ‐terminal protected α‐helical nonapeptides, each of which bears a His residue (a potential axial lig‐and of the iron ion) in the central position. In order to understand better the three‐dimensional structure of Fe III mimochrome I and its correlation with spectral properties, we have characterized the fully diamagnetic parent compound Co III mimochrome I by UV/visible, CD, and NMR spectroscopy, coupled with conformational energy calculations. Co III mimochrome I is a highly water‐soluble compound present in solution as two isomers, which slowly interconvert only at very low pH values. These isomers were isolated and separately characterized. Their UV/visible spectral properties are very similar, while their CD spectral properties differ markedly in both the far UV and Soret regions. The isomers were identified by 1 H NMR spectroscopy as diastereomers of the δ and δ type. This is the first example of an accurate three‐dimensional structure determination in solution of a hemoprotein mimetic that allows a straightforward correlation between structure and spectral properties.