Accessory pigment Accessory pigment Accessory pigments are light-absorbing compounds, found in photosynthetic organisms, that work in conjunction with chlorophyll "a". They include other forms of this pigment, such as chlorophyll "b" in green algal and higher plant antennae, while other algae may contain chlorophyll "c" or "d". In addition, there are many non-chlorophyll accessory pigments, such as carotenoids or phycobiliproteins, which also absorb light and transfer that light energy to photosystem chlorophyll. Some of these accessory pigments, in particular the carotenoids, also serve to absorb and dissipate excess light energy, or work as antioxidants. The large, physically associated group of chlorophylls and
Light-harvesting complexes of green plants protons and electrons. Under changing light conditions, the reversible phosphorylation of light harvesting chlorophyll a/b binding proteins (LHCII) represents a system for balancing the excitation energy between the two photosystems. The N-terminus of the chlorophyll A-B binding protein extends into the stroma where it is involved with adhesion of granal membranes and photo-regulated by reversible phosphorylation of its threonine residues. Both these processes are believed to mediate the distribution of excitation energy between photosystems I and II. This family also includes the photosystem II protein PsbS, which plays a role in energy-dependent quenching that increases thermal dissipation of excess absorbed