Premium
PROTECTION OF CHLOROPHYLL a BY CAROTENOID FROM PHOTODYNAMIC DECOMPOSITION
Author(s) -
Koka Prasad,
Song PillSoon
Publication year - 1978
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/j.1751-1097.1978.tb06959.x
Subject(s) - singlet oxygen , photochemistry , peridinin , chemistry , chlorophyll , photosynthesis , quenching (fluorescence) , dabco , pigment , carotenoid , chlorophyll a , triplet state , oxygen , octane , fucoxanthin , molecule , fluorescence , organic chemistry , biochemistry , physics , quantum mechanics
— The order of inhibition of the photooxidation of chlorophyll a in ethanol and ethanol‐benzene is as follows: β‐carotene, α‐tocopherol, benzoquinone, DABCO, menadione, cholesterol and KI. The quenching of singlet oxygen by β‐carotene occurs by a collisional quenching mechanism with a diffusion‐controlled rate of 1.7 × 10 10 M ‐1 s ‐1 . Photodecomposition of Chi a is faster in ethanol‐D 2 O than in ethanol‐H 2 O. Photoirradiation (660 nm) of the peridinin‐Chl a ‐protein complex, a photosynthetic light‐harvesting pigment isolated from marine dinoflagellates, did not show any photo‐decomposition of its Chi a in H 2 O or D 2 O, even after an extended period (12 h) of irradiation. However, the carotenoid, peridinin, in the photosynthetic antenna pigment was photobleached (ca. 10%) during the irradiation. We conclude that the singlet oxygen formed as a result of the Chi photosensitization is immediately quenched by the low‐lying triplet state of four peridinin molecules (per Chl a ) bound within the same protein crevice. The carotenoid thus effectively protects Chl a from photodynamic damage, providing a direct proof for the protective role of carotenoids in the photosynthetic pigment complex.