Reaction centers of Rhodobacter sphaeroides R-26 with selective replacement of bacteriopheophytin by pheophytin a: I. Characterisation of steady-state absorbance and circular dichroism, and of the P +Q A− state

Abstract

Bacteriopheophytin (BPheo) a of reaction centers (RCs) of Rhodobacter sphaeroides R-26 has been exchanged with pheophytin (Pheo) a. By varying the incubation temperature of the pigment exchange procedure two types of RCs were obtained, with either only the BPheo in the B-chain (BPheo B) or both BPheo B and BPheo A replaced by Pheo a. For the two RC types absorption and CD spectra at 6 K as well as P +Q A − difference spectra at 10 K are compared with those of native RCs. The most pronounced differences are observed in the Q Y and Q X regions of the (B)Pheos. The P +Q A − decay halftime is for RCs with Pheo a in both chains 10–15 ms longer than for native RCs and RCs that still have a BPheo in the A-chain, at all temperatures between 10 and 290 K. At low temperatures all three RC types showed biphasic P +Q A − recombination.