Resonance Raman spectroscopy study of protonated porphyrin.

Resonance Raman microscopy was used to study the resonance Raman scattering of the diacid (diprotonated form) of free-base porphyrin (21H,23H-porphine) in a crystal powder and KBr pellets. Intensive lines in the spectral range between 100÷1000cm have been detected and assigned as spectral manifestation of out-of-plane modes. The Raman spectra were simulated by means of DFT methods and compared with the experimental data.

Infrared absorption study of the heme pocket dynamics of carbonmonoxyheme proteins.

The temperature dependencies of the infrared absorption CO bands of carboxy complexes of horseradish peroxidase (HRP(CO)) in glycerol/water mixture at pH 6.0 and 9.3 are interpreted using the theory of optical absorption bandshape.

Probing the decay coordinate of the green fluorescent protein: arrest of cis-trans isomerization by the protein significantly narrows the fluorescence spectra.

The fluorescence spectra of the wild-type green fluorescence protein (wt-GFP) and the anionic form of p-hydroxybenzylidenedimethylimidazolone (p-HBDI), which models the protein chromophore, were obtained in the 80-300 K temperature range in glycerol/water solvent. The protein spectra have pronounced and well-resolved vibronic structure, at least at lower temperatures. In contrast, the chromophore spectra are very broad and structureless even at the lowest temperatures.

Correct interpretation of heme protein spectra allows distinguishing between the heme and the protein dynamics.

It is shown by using the vibronic approach that the iron displacement out of the porphyrin plane in deoxyheme proteins intermixes the porphyrin pi and axial iron-histidine sigma electronic subsystems. This intermixing explains the substantial coupling of the iron-histidine vibration to the heme Soret excitation, the appearance of the iron-histidine band in the corresponding resonance Raman spectra, and a number of other experimental data, including the dependence of the iron-histidine vibrational frequency on the extent of the iron displacement out of the porphyrin plane. This dependence implies that there is an anharmonic coupling between the corresponding vibrations, which is shown to be the cause of the specific temperature dependence of the iron-histidine band.