THE ASYMMETRY OF P+ IN BACTERIAL REACTION CENTERS REVEALED BY CIRCULAR-DICHROISM SPECTROSCOPY

The circular dichroism anisotropy, (A(L) - A(R))/A, has been measured for the far-red absorption band of P+ in reaction centers of two purple bacteria (Rhodopseudomonas viridis and Rhodobacter sphaeroides) and one green sulfur bacterium (Chlorobium tepidum). The anisotropy values for P960(+) (Rps. viridis) at 1310 nm was found to be +(13 +/- 2) x 10(-4). The corresponding value for P870(+) (Rb. sphaeroides) at 1250 nm was +(11 +/- 1) x 10(-4), but for P840(+) (C. tepidum) at 1160 nm the value was negative: -(27 +/- 2) x 10(-4). These results show that the configuration of the special pair in P840 is significantly different from the configuration in P870 and P960.