Abstract
Bacteriochlorophyll a solutions without and with carotenoids (in the 1:1 mole ratio) including neurosporene (the number of conjugated double bonds; n = 9), spheroidene (n = 10), lycopene (n = 11), anhydrorhodovibrin (n = 12) were irradiated with light (λ> 760 nm), and the bleaching of the Qy absorption was traced. The following results were obtained: (1) All the carotenoids exhibited the photo-protective function against the degradation of bacteriochlorophyll a. (2) The efficiency of the photo-protection in solution was exactly the same among the four carotenoids examined, irrespective of the conjugation light. This result contrasts to the case of the LH2 antenna complexes, and suggests different mechanisms. In solution, the collision of the excited-state bacteriochlorophyll a and the ground-state carotenoid molecules may play a most important role. We plan to examine the case when those pigment molecules are incooperated in the liposomes.
