Bacteriochlorophyll/imidazole

Bacteriochlorophyll/imidazole and chlorophyll/imidazole complexes. In a late 2000 report, de Groot and co-workers reported the results of a study of bacteriochlorophyll and chlorophyll complexes with imidazole that relied on long-range correlation... 

Spectral measurements suggesting exciton splitting were among early observations that led to the conclusion that the bacteriochlorophyll involved in the initial photochemical process exists as a dimer or special pair (Fig. 23-31),319/324 a conclusion verified by the structure determination. The special pair of BChl b lies in the center of the helical bundle that is embedded in the membrane. Nearly perpendicular to the rings of the special pair are two more molecules of BChl b. The central magnesium atoms of all four bacteriochlorophylls are held by imidazole groups of histidine side chains.319 325 Below the chlorophylls are... 

Although the axial histidine ligands interact strongly with the P+ and B" radicals, these interactions play only a minor role in the calculated free energy difference between P+Bm and P+Bl [H]. This is partly because the distances from the imidazole ligands to the bacteriochlorophylls are similar on the two sides of the reaction center, at least in the Rp. viridis crystal structure [15,16]. (There may be larger differences between these distances in the Rb. sphaeroides structure [23].) The amino acid residue that appears... 

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