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Characterization of 3‐Acetyl Chlorophyll a and 3‐Acetyl Protochlorophyll a Accommodated in the B800 Binding Sites of Photosynthetic Light‐Harvesting Complex 2 in the Purple Photosynthetic Bacterium Rhodoblastus acidophilus
Author(s) -
Saga Yoshitaka,
Miyagi Kanji
Publication year - 2018
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12919
Subject(s) - bacteriochlorophyll , tetrapyrrole , light harvesting complex , photosynthesis , porphyrin , chemistry , chlorophyll a , chlorophyll , photochemistry , rhodospirillaceae , absorbance , photosynthetic reaction centre , binding site , stereochemistry , biochemistry , organic chemistry , chromatography , photosystem ii , enzyme
We present the detailed characterization on the reconstitution of two cyclic tetrapyrrole pigments that have the same substituents but differ in the degree of hydrogenation in the macrocycles from bacteriochlorophyll ( BC hl) a (7,8,17,18‐tetrahydroporphyrin) into the binding sites of B800 BC hl a in light‐harvesting complex 2 ( LH 2) of purple photosynthetic bacteria. Both 3‐acetyl chlorophyll (Chl) a (17,18‐dihydroporphyrin) and 3‐acetyl protochlorophyll ( PC hl) a (porphyrin) were inserted into the B800‐binding pockets in LH 2, indicating that these pockets allow alteration of the degree of hydrogenation in the cyclic tetrapyrroles. Redshifts of the Q y peak positions of 3‐acetyl (P)Chl a by insertion into the B800‐binding sites were smaller than that of BC hl a . The relative Q y absorbance of 3‐acetyl (P)Chl a to B850 BC hl a in the reconstituted proteins was significantly smaller than that of B800 BC hl a in native LH 2 in spite of their high occupancy in the B800‐binding sites. These are ascribable to the smaller dipole strengths of 3‐acetyl (P)Chl a . We also performed the coreconstitution of both 3‐acetyl Chl a and BC hl a into the nine B800‐binding sites in LH 2, indicating that the affinity of 3‐acetyl Chl a to the B800‐cavity was slightly higher than that of BC hl a .