RESONANCE-ENHANCED CARS SPECTROSCOPY OF BILIPROTEINS - A COMPARISON BETWEEN PHYCOERYTHROCYANIN AND PHYCOCYANIN OF MASTIGOCLADUS-LAMINOSUS

Resonance-enhanced coherent anti-Stokes Raman (CARS) spectra are repor ted for trimers of phycoerthrocyanin (PEC) dissolved in H2O and D2O. T he CARS spectra are significantly different when recorded with pump wa velength either at 585 mn or 630 nm. By comparison of the 630 nm spect ra with those of phycocyanin one can conclude that there is a change i n the relative location of the lowest excited states of the beta 84 an d beta 155 chromophores. Upon additional illumination with 514.5 nm la ser light, only the spectra recorded with 585 nm pump wavelength chang e. This is in accordance with earlier observations that the phycoviolo bilin chromophore of the alpha-subunit exhibits photochromic behavior. The changes in the CARS spectra provide evidence that it is the methi ne bridge between rings C and D that undergoes the geometrical changes . Furthermore, it is suggested that there are different types of photo induced rearrangements operative and that the isomeric distribution is different in H2O and D2O.