Abstract
Carotenoids (Cars) play the photo-protective function against photo-degradation. We examined the effect of Car on the photo-degradation of bacteriochlorophyll (BChl). We irradiated the reaction center (RC) from Rhodobacter sphaeroides R26.1, Ga and 2.4.1 with light (λ > 760 nm), and traced the bleaching of the special-pair bacteriochlorophylls (P) as well as BChls in solution and bound to LH2. We have obtained the following results: (1) BChl a transfers into 3-acetyl-Chl a in solution by photo-oxidation. This is suppressed by the addition of Car, but not depending on the number of the conjugated double bonds (n). (2) The same reaction happens at P in RC as well as in LH2, and the suppression increases with increasing n. The results show that the photo-protective function against the oxidation reaction by Cars can take place efficiently with increasing n in those pigment-protein complexes.
