Fluorescence decay kinetics of wild type and D2-H117N mutant photosystem II reaction centers isolated from Chlamydomonas reinhardtii

We compare the chlorophyll fluorescence decay kinetics of the wild type and the D2-H117N mutant photosystem II reaction centers isolated from Chlamydo monas reinhardtii. The histidine residue located at site 117 on the D2 poly peptide of photosystem II is a proposed binding site for one of two periphe ral accessory chlorophylls located in the reaction center complex. The peri pheral accessory chlorophylls are thought to be coupled with the primary el ectron donor, P680, and thus involved in energy transfer with P680, The con servative replacement of the histidine residue with an asparagine residue a llows the chlorophyll to remain bound to the reaction center. However, slig ht changes in the structural organization of the reaction center may exist that can affect the energy transfer kinetics. We show that the D2-H117N mut ation causes a shift in the 20-30 ps lifetime component that has been assoc iated with energy equilibration among coupled chlorophylls in the photosyst em II reaction center.