Fig. 1. Component absorbance, emission and mechanism.

a Thylakoid membranes from oxygenic phototrophs such as pea and chromatophore membranes from anoxygenic phototrophs such as Rba. sphaeroides have complementary absorbance spectra due to differences in the electronic structures of the macrocycle π electron systems of chlorophyll and bacteriochlorophyll (see also Supplementary Fig. 1). b The major plant light-harvesting complex LHCII harvests solar energy in regions where absorbance by Rba. sphaeroides RCs is weak, notably around 650 nm, and its emission spectrum overlaps the absorbance spectrum of the RC between 640 and 800 nm. c The red-enhanced emission spectrum of heterodimeric plant LHCI has a stronger overlap with the absorbance spectrum of the Rba. sphaeroides RC, particularly the coincident absorbance bands of the bacteriopheophytins (H_A/H_B). d Architecture of the RC cofactors and the route of four-step charge separation which oxidises P870 and reduces Q_B. The bacteriochlorophylls (orange carbons) and bacteriopheophytins (yellow carbons) give rise to the absorbance bands labelled in c. Further descriptions of pigment-protein structures and their sources are given in Supplementary Fig. 1.