SPECTROSCOPIC CHARACTERIZATION OF 2 FORMS OF THE D1-D2-CYTOCHROME B559 COMPLEX FROM SUGAR-BEET

Two D1-D2-cytochrome b559 complex forms, called RCIIa and RCIIb, with different pigment stoichiometry were characterized using absorption an d surface-enhanced resonance Raman scattering spectroscopy and spectra l gaussian deconvolution. Electronic absorption spectra of the RCIIb a t 277 K showed significant differences compared to RCIIa, i.e. a stron g decrease in the absorbance due to carotenoid and chlorophyll for the same amount of pheophytin. A reduced carotenoid and chlorophyll conte nt in RCIIb was also observed in the surface-enhanced resonance Raman scattering spectra. Spectral deconvolution elicited three main absorpt ion bands at 680, 672 and 669-670 nm, which were ascribed to P680, phe ophytin and accessory chlorophyll, respectively. In addition, a minor component around 667 nm was observed in the RCIIb, most probably due t o some reaction center inactivation. Calculation of the relative area under the gaussians together with pigment stoichiometry data suggest t hat the 680, 672 and 669-670 nm components contain, respectively, two chlorophylls, two pheophytins and four chlorophylls for the RCIIa, and two chlorophylls, two pheophytins and two chlorophylls for the RCIIb.