Fourier transform near-infrared resonance Raman spectroscopic study of the α-subunit of phycoerythrocyanin and phycocyanin from the cyanobacteriumMastigocladus laminosus

The isolated alpha-subunits of the light-harvesting pigments phycoerythrocyanin (PEC) and C-phycocyanin (CPC) of Mastigocladus laminosus were studied by resonance Raman (RR) spectroscopy, The results for PEC indicate that the photoconversion of the tetrapyrrole chromophore from the Z,Z to the Z,E configuration is associated with structural changes which are largely restricted to the photoisomerization site, i.e. the methine-bridge C-D. Evidently the rotation around this double bond is not complete in the first intermediate which can be detected after the photochemical event. The subsequent decay to the stable Z,E isomer at T > -30 degrees C is associated with conformational relaxations of the remainder of the chromophore, Thus, the PEC photoconversion differs substantially from that of the plant photoreceptor phytochrome, which exhibits more extended changes of the chromophore structure and its interactions with the protein environment during the photoconversion. (C) 1998 John Wiley & Sons, Ltd.