chlorophyll and chlorophyll-f

We prepared thylakoid membranes from Halomicronema hongdechloris cells grown under white fluorescent light or light from far-red (740 nm) light-emitting diodes, and observed their energy-transfer processes shortly after light excitation. Excitation-relaxation processes were examined by steady-state and time-resolved fluorescence spectroscopies. Two time-resolved fluorescence techniques were used: time-correlated single photon counting and fluorescence up-conversion methods. The thylakoids from the cells grown under white light contained chlorophyll (Chl) a of different energies, but were devoid of Chl f. At room temperature, the excitation energy was equilibrated among the Chl a pools with a time constant of 6.6 ps. Conversely, the thylakoids from the cells grown under far-red light possessed both Chl a and Chl f. Two energy-transfer pathways from Chl a to Chl f were identified with time constants of 1.3 and 5.0 ps, and the excitation energy was equilibrated between the Chl a and Chl f pools at room temperature. We also examined the energy-transfer pathways from phycobilisome to the two photosystems under white-light cultivation.

Topics: Chlorophyll; Chlorophyll A; Cyanobacteria; Energy Transfer; Fluorescence; Light; Light-Harvesting Protein Complexes; Phycobilisomes; Spectrometry, Fluorescence; Thylakoids

Chlorophyll f (1) is the most red-shifted absorbing natural chlorophyll reported, and it is assigned the structure [2-formyl]-chlorophyll a (C55H70O6N4Mg). This structural assignment is confirmed based on the relative retention time on HPLC, mass spectroscopy, UV/vis absorption, and CD spectroscopy, and proton and carbon NMR of chlorophyll f purified from Halomicronema hongdechloris.

Topics: Chlorophyll; Chromatography, High Pressure Liquid; Cyanobacteria; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular