Temperature dependent hole burning of the 684 nm chlorophyll a of the isolated reaction center of Photosystem II: confirmation of the linker model Original Research Article

Currently the nature of the additional chlorophyll a (Chl a) molecules which take the number of Chl a per isolated D1-D2-cyt b559 complex beyond the value of four for the bacterial reaction center is a subject of much importance and interest. Chang et al. [J. Phys. Chem. 98 (1994) 7725], who studied preparations of this complex with significantly different Chl a contents, concluded that the 684 nm absorbing Chl a contribute to the additional Chl a and proposed that they are of the linker type, serving to shuttle energy from the proximal antenna complex to the reaction center. Implicit in this model is that the 684 nm Chl a communicate with the primary electron donor Chl a (P680) via energy transfer and that the resulting detrapping of the Qy-state of the 684 nm Chl a should depend strongly on temperature. Temperature dependent transient hole spectra are presented that are in complete accord with this prediction. Theoretical calculations on the kinetics and temperature dependence of the hole profile of the 680 nm absorption band are presented and provide convincing support for the linker model. The data are argued to be inconsistent with other models.