Z,E isomerization of the α‐84 phycoviolobilin chromophore of phycoerythrocyanin from Mastigocladus laminosus investigated by Fourier‐transform infrared difference spectroscopy

摘要

>The photoreaction of the phycoviolobilin (PVB) chromophore-containing part of phycoerythrocyanin (PEC) from Mastigocladus laminosus was investigated by Fourier-transform infrared spectroscopy (FT-IR). Difference spectra between the parent states P566 and P507 were obtained in 1H₂O and 2H₂O for the first time. The spectra are generally characterised by large changes in the range between 1710 and 1590 cm−1 and by a strong difference band around 1270 cm−1. In order to study the influence on the PVB chromophore upon aggregation, spectra of the α-subunit and the (αβ)₃ trimer are compared, showing distinct differences which may be of relevance for the chromophore-protein and protein-protein interactions. The difference spectra demonstrate many similarities to the spectra recently obtained for the P_r→meta-R_c transition of phytochrome [Foerstendorf et al. (1996) Biochemistry 35, 10793–10799]. In particular, a band around 1710 cm−1, which was tentatively assigned to the C=O stretch of ring D is also observed in the spectra of PEC. It strongly supports this identification and the deduced molecular interpretation on the protonation state of the chromophore.