Energy transfer in the light-harvesting complex II of Dunaliella tertiolecta is unusually sensitive to Triton X-100

Isolation of membrane bound light-harvesting-complexes from the dinoflagellates Heterocapsa pygmaea and Prorocentrum minimum

We have isolated Chl a-Chl c-carotenoid binding proteins from the dinoflagellates Prorocentrum minimum and Heterocapsa pygmaea grown under high (500 μmol m(-2) s(-1), HL) and low (35 μmol m(-2) s(-1), LL) light conditions. We compared various isolation procedures of membrane bound light harvesting complexes (LHCs) and assayed the functionality of the solubilized proteins by determining the energy transfer efficiency from the accessory pigments to Chl a by means of fluorescence excitation spectra. The identity of the newly isolated protein-complexes were confirmed by immunological cross-reactions with antibodies raised against the previously described membrane bound Chl a-c proteins (Boczar et al. (1980) FEBS Lett 120: 243-247). Spectroscopic analysis demonstrated the relatedness of these proteins with the recently described Chl-a-c 2-peridinin (ACP) binding protein (Hiller et al. (1993) Photochem Photobiol 57: 125-131; Iglesias Prieto et al. (1993) Phil Trans R Soc London B 338: 381-392). The water-soluble peridinin-Chl a binding-protein (PCP) was not detectable in P. minimum. Two functional forms of ACP with different pigmentation were isolated. A variant of ACP which was isolated from high-light grown cells, that specifically binds increased amounts of diadinoxanthin was compared to the previously described ACPs that bind proportionately more peridinin.

Effects of detergent on the excited state structure and relaxation dynamics of the photosystem II reaction center: A high resolution hole burning study

Low temperature (4.2 K) absorption and hole burned spectra are reported for a stabilized preparation (no excess detergent) of the photosystem II reaction center complex. The complex was studied in glasses to which detergent had and had not been added. Triton X-100 (but not dodecyl maltoside) detergent was found to significantly affect the absorption and persistent hole spectra and to disrupt energy transfer from the accessory chlorophyll a to the active pheophytin a. However, Triton X-100 does not significantly affect the transient hole spectrum and lifetime (1.9 ps at 4.2 K) of the primary donor state, P680(*). Data are presented which indicate that the disruptive effects of Triton X-100 are not due to extraction of pigments from the reaction center, leaving structural perturbations as the most plausible explanation. In the absence of detergent the high resolution persistent hole spectra yield an energy transfer decay time for the accessory Chl a QY-state at 1.6 K of 12 ps, which is about three orders of magnitude longer than the corresponding time for the bacterial RC. In the presence of Triton X-100 the Chl a QY-state decay time is increased by at least a factor of 50.