EFFECTS OF ZWITTERIONIC DETERGENTS ON THE ELECTRONIC-STRUCTURE OF THEPRIMARY DONOR AND THE CHARGE RECOMBINATION KINETICS OF P(-) IN NATIVEAND MUTANT REACTION CENTERS FROM RHODOBACTER-SPHAEROIDES()Q(A)()

The effects of detergents on the electronic structure of the oxidized primary donor P+ and the time constant tau(AP) of the P(+)Q(A)(-) char ge recombination at ambient temperatures have been investigated in nat ive and mutant reaction centers (RCs) from Rhodobacter sphaeroides. It is shown that N-lauryl-N,N-dimethyl-3-ammonio-1-propane sulfonate (SB 12) induces a transition to a second distinct conformation of the RC. In the case of the wild type and the mutant FY(M197), in which a hydr ogen bond is introduced to the 2-acetyl group of the dimer half of P t hat is associated with the M-subunit of the RC, the conformational cha nge causes a more asymmetric spin density distribution between the two bacteriochlorophyll moieties of P+ in favor of the L-half. For both t ypes of RCs the time constant tau(AP) depends on the SB12/RC ratio as does the position of the long-wavelength band of P, lambda(max). The i ncrease of tau(AP) by similar to 30 ms and the shift of lambda(max) fr om similar to 866 nm to similar to 851 nm are indicative for the confo rmational change. In addition, a smaller linear increase of tau(AP) wi th increasing SB12/RC ratio is superimposed on the variation of tau(AP ) due to the conformational change. Similar effects of SB12 on the opt ical spectra as well as on tau(AP) are also observed for the two heter odimer mutants HL(L173) and HL(M202), in which one of the bacteriochlo rophylls of P is replaced by a bacteriopheophytin. There are no clear indications for a correlation of tau(AP) With the localization of the positive charge in P+. Furthermore, it is concluded from the dependenc e of tau(AP) On the SB12/RC ratio that the single-site mutations do no t affect the standard free energy difference of the two conformations to a measurable extent.