THE CONFIGURATION OF BETA-CAROTENE IN THE PHOTOSYSTEM-II REACTION-CENTER

Different pigment extraction procedures and HPLC methods were tested t o investigate the geometric configuration of the beta-carotene in two forms of the photosystem II reaction center (D1-D2-cytochrome (Cyt) b5 59) complex containing one and two beta-carotene molecules per two phe ophytin a. All the handling steps and HPLC analyses were done in darkn ess at room temperature and at 4 degrees C, Two different pigment extr acts were analyzed, a mixture of chlorophyll a, pheophytin a and beta- carotene, and the isolated beta-carotene from that mixture. In both ca ses only the all-trans-beta-carotene was detected. The chromatographic profiles were similar at both temperatures only differing in the rete ntion times that were longer at 4 degrees C. This result was independe nt of the concentration of photosynthetic starting material. Furthermo re, no differences were observed between D1-D2-Cyt b559 complexes with one and two beta-carotene molecules per reaction center. The analysis of the beta-carotene chromatographic peak indicated no 15-cis to all- trails isomerization occurred during the HPLC chromatography in our ex perimental conditions. Resonance Raman spectra were also recorded in t he isolated D1-D2-Cyt b559 complex at room and liquid nitrogen tempera ture with excitation at 514.5 nm from an Ar+ laser. Spectra of control preparations showed main bands at 1532, 1264, 1213, 1185, 1154 and 10 03 cm(-1) corresponding to the all-trans isomer and confirm previous r esults. The presence in the reaction center suspension of artificial e lectron accepters such as silicomolybdate or 2,5-dibromo-3-methyl-6-is opropyl-p-benzoquinone that are able to quench (3)P680 did not modify the resonance Raman spectra of the native D1-D2-Cyt b559 complex. The results suggest that no isomerization takes place during the laser irr adiation.