Fluorescence of light-harvesting chlorophyll a/b-protein complexes: implications for the photosynthetic unit.

To the extent that extracted light-harvesting chlorophyll proteins (LHCPs) retain the chlorophyll configuration which they had in vivo, information on the optical properties of LHCPs is useful for an assessment of the transfer process of the primary excitation energy in photosynthesis. Within this context we report and discuss the implication of three kinds of data on spinach chloroplast LHCP. First, an analysis of the spectroscopic dependence of absorption, polarization and circular dichroism (reported recently by R.L.V.) suggests a model affording the possibility of easy chlorophyll a intercomplex transfer with chlorophyll b groups acting as local antitraps. Second, the ratio of LHCP emission and absorption probabilities obeys the Stepanov relation over a relatively wide range, an observation which suggests rapid Chl b-Chl a excitation equilibration. Finally, an LHCP absolute fluorescence yield as great as 10% has been measured, which provides a possible upper limit for the yield of the antenna fluorescence.