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

Yoshitaka Saga*, Kanji Miyagi

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

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 (BChl) a (7,8,17,18-tetrahydroporphyrin) into the binding sites of B800 BChl a in light-harvesting complex 2 (LH2) of purple photosynthetic bacteria. Both 3-acetyl chlorophyll (Chl) a (17,18-dihydroporphyrin) and 3-acetyl protochlorophyll (PChl) a (porphyrin) were inserted into the B800-binding pockets in LH2, indicating that these pockets allow alteration of the degree of hydrogenation in the cyclic tetrapyrroles. Redshifts of the Qy peak positions of 3-acetyl (P)Chl a by insertion into the B800-binding sites were smaller than that of BChl a. The relative Qy absorbance of 3-acetyl (P)Chl a to B850 BChl a in the reconstituted proteins was significantly smaller than that of B800 BChl a in native LH2 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 BChl a into the nine B800-binding sites in LH2, indicating that the affinity of 3-acetyl Chl a to the B800-cavity was slightly higher than that of BChl a.

Original languageEnglish
Pages (from-to)698-704
Number of pages7
JournalPhotochemistry and Photobiology
Volume94
Issue number4
DOIs
Publication statusPublished - 1 Jul 2018
Externally publishedYes

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