Reaction centers of Rhodobacter sphaeroides R-26 with selective replacement of bacteriopheophytin by pheophytin alpha .1. Characterisation of steady-state absorbance and circular dichroism, and of the P(+)Q(A)(-) state

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.