ENERGY TRANSFER IN A LIGHT-HARVESTING CAROTENOID-CHLOROPHYLL c-CHLOROPHYLL a-PROTEIN OF PHAEODACTYLUM TRICORNUTUM

Abstract— The marine diatom Phaeodactylum tricornutum was readily disrupted in 0.1 N Tris-HCl buffer, pH 7.8, in a Braun Model MSK cell homogenizer at 0-5°C. Treatment of the suspension with sodium lauryol sarcosinate (3 molecules per 10000 daltons of protein) at 5°C in the dark and subsequent centrifugations produced a pigmented, protein fraction whose excitation spectrum exhibited energy transfer from carotenoids to chlorophyll a (Chi a ). Disruption of the pigment-protein complex by heating in 1% sodium dodecylsulfate resulted in loss of energy transfer. For each Chi a molecule this fraction had 1 Chi c , 4 fucoxanthin, and 6.7 accessory pigment molecules. Presence of the accessory complex of Photosystem II in this preparation is suggested by the high xanthophyll content. Further, based on Chl a concentrations, this fraction had about 18 times more apparent fluorescence emission at 680 nm when excited at 470 nm than the intact cells.