Influence of magnetic fields on the P-870 triplet state in Rps. sphaeroides reaction centers.

Magnetic fields influence two properties of the P-870 triplet state observed in Rps. sphaeroides reaction centers: the yield of formation and the kinetics of decay. These effects have been studied in reaction centers which were prepared in three different states: state QA (-), state QA (2-) and state (- QA) (QA depleted). The triplet yields decrease with increasing magnetic fields, with B1/2's of about 140, 41 and 57 Gauss, respectively. The half-time of (3)P-870 decay is not influenced by the field in state QA (-); it increases at increasing fields, in state QA (2-) and state (- QA), with the same B1/2 as the triplet yield. These results are discussed in the framework of current theories of the radical-pair dynamics and of the mechanism of triplet decay.