bacteriochlorofyl

Bacteriochlorophylls are a family of chlorophyll-like pigments produced by photosynthetic bacteria. They act as primary light-harvesting pigments in anoxygenic photosynthesis, absorbing light mainly in the near-infrared and transferring energy to reaction centers. Compared with the chlorophylls of plants and cyanobacteria, they have a more reduced porphyrin backbone and different side chains, which shift absorption to longer wavelengths.

Bacteriochlorophylls occur in several groups of bacteria, notably purple sulfur and purple non-sulfur bacteria (Proteobacteria) and green sulfur bacteria. In purple bacteria they are major components of the light-harvesting antennae (such as LH1 and LH2) and participate in reaction centers. In green sulfur bacteria chlorosomes contain bacteriochlorophylls c, d and e, enabling light capture under very dim conditions and energy transfer to the reaction center via baseplate and the Fenna–Matthews–Olson protein in some systems.

Diversity: The family includes bacteriochlorophyll a and b, as well as chlorosome-associated c, d and e types. They differ in the substitutions on the porphyrin ring and in the hydrophobic side chains, which affects absorption properties and membrane organization. Absorption maxima extend into the near-infrared, depending on the variant and organism.

Chemistry and biosynthesis: BChls share the chlorophyll tetrapyrrole core and Mg2+ center, and typically bear a hydrophobic isoprenoid tail for membrane anchoring. Biosynthesis proceeds from common tetrapyrrole precursors; specific reductions and substitutions produce the bacteriochlorin forms and the distinct side chains of BChl a, b, c, d and e.

Significance: Bacteriochlorophylls are central to the physiology of anaerobic photosynthetic bacteria and provide insight into natural light harvesting and energy transfer. They are studied for understanding photosynthesis and for explorations of bio-inspired solar-energy concepts.