Modified reaction centers from Rhodobacter sphaeroides R26

Abstract

Incubation of photosynthetic reaction centers from Rhodobucter sphaeroides R26 with exogenous lY-OH-bacteriochlorophyll ar or aoo according to Scheer et al. (1987) results in the exchange of endogenous bacteriochlorophyll ar. The exchange amounts to 5 50% according to HPLC analysis, corresponding to a complete replacement of the 'monomeric' bacteriochlorophylls, Bu and Br, by exogenous pigment. The absorption spectra show small, but distinct changes in the Qx-region of the bacteriochlorophylls, and bleaching of the modified reaction centers is retained. The corresponding binding sites must be accessible from the exterior, and allow for the introduction of a polar residue at C-1P. This is supported by the observation of side reactions of the endogenous 'monomeric' bacteriochlorophylls within the reaction center pigments, e.g. epimerization and hydroxylation at C-l32.

Modified bacterial reaction centers. 4. The borohydride treatment reinvestigated: comparison with selective exchange experiments at binding sites BA,B and HA,B

“…As mentioned in the previous section, this band is absent if carefully purified RC are treated. Small amounts of BChi a' (peak B) in the pigment extract of borohydride-treated reaction centers are as observed in other treatments [18] and cannot explain the changes in the absorption spectrum, either.…”

“…No reduction of the 13t-C = O group [27][28][29] was observed, even after prolonged standing and repeated addition of the reagent. Partial exchange with 3t-OH-BChl a of monomeric BChI a at the B^.n binding sites [18,19] yields RC with the absorption spectrum shown in Fig. ld [19].…”

“…Today there are several possibilities available to modify either the amino-acid [10][11][12][13][14][15][16] and/or the pigment composition [17][18][19][20]. Historically, however, treatment with borohydride was the first method by which reaction centers from Rb.…”

Primary electron transfer kinetics in bacterial reaction centers with modified bacteriochlorophylls at the monomeric sites BA,B.

“…The preparation of RCs containing the modified [3-vinyl]-132-hydroxy-BChl-a shows a substantially different absorption spectrum from native RC ( This shoulder is due to an incomplete exchange (80%o) of the monomeric BChl-a. Part of this shoulder may also be due to the upper excitonic component of the Q(P) band (22,25,26).…”

Femtosecond Spectroscopy of the Primary Electron Transfer in Photosynthetic Reaction Centers

“…sphaeroides strain R26.1 desolved in glycerol (56 % v/v). RCs containing [3-vinyl]-132-hydroxy-bacteriochlorophyll a were prepared after Struck et al [14,15]. The BChl a exchange yielded values of 40 ± 5 %.…”