Abstract
During the catalytic step immediately prior to O-O bond formation in Photosystem II, a water molecule deprotonates and moves next to the water-splitting Mn4CaO5 cluster's O5 oxo bridge. Considerable evidence identifies O5 as one of the two substrate waters that ultimately form O2. The relocated oxygen, known as O6 or Ox, may be the second. It is currently debated whether O6 or Ox originates as the Mn-bound water denoted W2 or as the Ca2+-bound water denoted W3. To distinguish between these two possibilities, we analyzed the D-O-D bending mode of the water molecule that deprotonates/relocates to become O6/Ox. We show that this D-O-D bending mode is not altered by the D1-S169A mutation. Previously, we showed that this D-O-D bending mode is altered substantially when Sr2+ is substituted for Ca2+. Because Sr2+/Ca2+ substitution alters this D-O-D bending mode but the D1-S169A mutation does not, we conclude that the water-derived oxygen that relocates and becomes O6/Ox derives from the Ca2+-bound W3. This conclusion provides an important constraint for proposed mechanisms of O-O bond formation in Photosystem II.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
