Low temperature optical spectroscopy of cobalt-substituted hemocyanin from Carcinus maenas |
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Authors: | Eugenio Vitrano Antonio Cupane Maurizio Leone Valeria Militello Lorenzo Cordone Benedetto Salvato Mariano Beltramini Luigi Bubacco Gian Paolo Rocco |
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Institution: | (1) Istituto di Fisica dell'Università di Palermo and GNSM-JNFM, via Archirafi 36, I-90123 Palermo, Italy;(2) Dipartimento di Biologia dell'Università di Padova, via Trieste 75, I-35121 Padova, Italy;(3) CNR Centro per le Emocianine e altre metalloproteine, via Trieste 75, I-35121 Padova, Italy;(4) Present address: Albert Einstein College of Medicine, Yeshiva University, 10461 Bronx, NY, USA |
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Abstract: | In this work we report the optical absorption spectra of three cobalt-substituted derivatives of hemocyanin (He) from Carcinus maenas, in the temperature range 300–20 K. The derivatives studied are the mononuclear (Co2+)-He with a single cobalt ion in the CuA site, the binuclear (Co2+)2-He and the binuclear mixed metal (Co2+-Cu1+)-He. At low temperature three main bands are clearly resolved; the temperature dependence of their zeroth, first and second moments sheds light on the stereodynamic properties in the surroundings of the chromophore. Within the limits of the reported analysis, in the binuclear derivatives the motions coupled to the chromophore appear to be essentially harmonic in the whole temperature range investigated; moreover the data are consistent with the presence of an exogenous ligand strongly bound to the two metal ions. For the mononuclear derivative an essentially harmonic behavior is evident only up to 200 K where the data are consistent with the presence of an exogenous ligand much less strongly bound, while at higher temperatures the behavior of the spectra indicates the onset of very large anharmonic contributions to motions, that plausibly involve the above exogenous ligand and, quite likely, the entire active site.Abbreviations He
Hemocyanin
- M0
zeroth moment
- M1
first moment
- M2
second moment
- (Co2–)2-He
binuclear bicobalt hemocyanin derivative
- (Co2+)-He
mononuclear monocobalt hemocyanin derivative
- (Co2+-Cu1+)-He
binuclear mixed metals hemocyanin derivative
- LFT
ligand field theory
- CT
charge transfer
- EPR
electronic paramagnetic resonance
- XANES
X-ray absorption near edge structure
Correspondence to: L. Cordone |
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Keywords: | Hemocyanin Optical spectra Vibrational coupling |
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