Does LHCPII have a Long Wavelength Chlorophyll a Spectral Forms?
The absorption spectra of photosynthetic membranes show a complexity that can be interpreted as being due to the presence of different spectral forms of chlorophyll a (chla) (1), having the same chemical structure but with their spectral properties modified by local effects (2). The wavelength spacing between neighbour spectral species of chl is in the range 7–11nm, an energy difference that, due to a similar Stokes shift, determines a maximum Forster overlap integral between “sequential” forms of chls (3). The transfer of excitation energy from the peripheral antenna towards the RCs is usually described in terms of the dipole-dipole R−6 theory of Forster (4). It is therefore necessary to understand the absorbance of the chls in the native state in order to appreciate their role in the photosynthetic apparatus. To this end the decomposition of the absorption spectra of photosynthetic membranes or chl-protein complex preparations in a linear combination of gaussians, has become a technique to interpret the complexity of the membrane absorption spectra in terms of different spectral species of chla (5–8).
KeywordsPhotosynthetic Membrane Spectral Form 683nm Band Peripheral Antenna PSII Preparation
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