I am confused regarding the existence of special pair (primarily regarding PS2). Do both, P680 and P700 have special pair?
I have checked various sources online and have come across conflicting information. For instance wikipedia article on Photosystem (https://en.m.wikipedia.org/wiki/Photosystem_II) says:
Unlike the reaction centers of all other photosystems which have a special pair of closely spaced chlorophyll molecules, the pigment that undergoes the initial photoinduced charge separation in PSII is a chlorophyll monomer.
This is hyperlinked to a study by AW Rutherford which says:
It is proposed that the key event in the evolution of PSII was a mutation that resulted in the separation of the two pigments that made up the special chlorophyll pair, making them into two chlorophylls that were neither special nor paired.
However, Voet and Voet 4ed says that there are two Chla molecules that are analogous to the special pair seen in Photosynthetic Bacteria Reaction Centre (PBRC).
Additionally, I found this (http://www.life.illinois.edu/crofts/ahab/psiistrc.html)
The nature of P680 (the primary donor Chl) is still controversial. The dimeric special pair expected from bacterial centers has not been unambiguously demonstrated, although H198 of D1, and the equivalent in D2, are conserved as putative ligands, and the near IR band of P680+ is diagnostic. Several suggestions have been made that P680 might be monomeric (8-10), and more equivalent to the ancillary Chls of the bacterial reaction center.
The article is not dated unfortunately but I checked that all the citations are prior to 2000.