KINETIC-ANALYSIS OF ENERGY-TRANSFER PROCESSES IN LHC-II ISOLATED FROMTHE SIPHONOUS GREEN-ALGA, BRYOPSIS-MAXIMA WITH USE OF PICOSECOND FLUORESCENCE SPECTROSCOPY

Energy transfer processes among photosynthetic pigments of LHC II isol ated from a siphonous green alga, Bryopsis maxima were kinetically ana lyzed by picosecond time-resolved fluorescence spectroscopy. Plural tr ansfer pathways to Chi a were kinetically confirmed. At -196 degrees C , two carotenoids unique in this class of alga, siphonaxanthin and sip honein, transferred energy directly to only one Chi a form, Ca672. Ene rgy was finally transferred to Ca679 with a rate constant of about 20 ps, which was also evident from the red-shift of the emission maximum. At physiological temperature (15 degrees C), fluorescence from all Ch i a forms (Ca664, Ca672, Ca679 and Ca688) was observed immediately aft er siphonaxanthin excitation and relative intensities remained unchang ed during measurement. Excitation energy is thus transferred from the carotenoids to Chi a and is equilibrated among Chl a molecules. Chl b excitation gave rise to higher relative intensities of short wavelengt h forms of Chl a (Ca664 and Ca672) in an earlier time range, thus indi cating energy flow from Chl b to be mediated by Ca664 and then to Ca67 2. Similar time behavior of short wavelength forms of Chl a was detect ed in spinach LHC II, suggesting essentially identical energy migratio n processes in spinach LHC II. Based on their peptide sequence and opt ical properties, the molecular arrangement of pigments is discussed fo r LHC II isolated from Bryopsis and spinach.