REACTION CENTERS OF RHODOBACTER-SPHAEROIDES R-26 WITH SELECTIVE REPLACEMENT OF BACTERIOPHEOPHYTIN BY PHEOPHYTIN-ALPHA .1. CHARACTERIZATION OF STEADY-STATE ABSORBENCY AND CIRCULAR-DICHROISM, AND OF THE P(-) STATE()Q(A)()

Bacteriopheophytin (BPheo) a of reaction centers (RCs) of Rhodobacter sphaeroides R-26 has been exchanged with pheophytin (Pheo) a. By varyi ng the incubation temperature of the pigment exchange procedure two ty pes of RCs were obtained, with either only the BPheo in the B-chain (B Pheo(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)(-) diff erence 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 t he (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 hav e 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)(-) recomb ination.