Cryoprotectant-induced quenching of chlorophyll a fluorescence from light-harvesting complex 2 in vitro: Time-resolved fluorescence and steady state spectroscopic studies

Polyalcohols introduced efficient dissipative channels leading to a decrease of the average fluorescence lifetime from 4.3 to 1.0-0.6 ns, and the appearance of long-wavelength forms in the Iow-temperature fluorescence emission spectra, owing to the formation of aggregates. Aggregated light-harvesting chlorophyll-protein complex 2 (LHC2) suitable for the low-temperature absorption spectroscopy was obtained by incubation of a solubilized sample with ethylene glycol. Only a minor difference (red shift of about I nm which can be attributed to changes of the trimer conformation due to the aggregation) was observed between the absorption spectra of aggregated and solubilized LHC2 at 4 K. Thus, no indications were found for the formation of new long-wavelength chlorophyll forms in this type of aggregated LHC2.