Spectral Properties of Isolated Photosystem II Reaction Center Complex at 77K

Abstract

Among the many similarities noted between the isolated bacterial and photosystem II (PSII) reaction center (RC) complexes are analogous electron transport components [1], protein sequence homologies [2], and charge separation rates [3]. On the other hand, there are some striking differences. For example, the PSII RC contains Mn-binding sites not reported for the bacterial RC which is consistent with the O2-evolution role of PSII [4], the triplet state of chlorophyll (Chl) in the PSII RC is monomeric and oriented perpendicular to the analogous bacteriochlorophyll (BChl) triplet observed in the bacterial RC [5], and the excited singlet state lifetime of P680 (the primary donor in PSII) is much longer than that reported for P870 (the primary donor in the RC of purple bacteria) [3]. Furthermore, whereas P870 is red-shifted up to 100 nm compared to the other porphyrins in the bacterial RC, P680 is red-shifted about 10 nm, and there is significant spectral overlap between all of the PSII pigments in red region. Consequently, the purpose of this paper is to further examine the spectral properties of stabilized PSII RC complex with emphasis on the nature of the primary donor.