# g , $$f = \left( {{\frac{{{\raise0 7ex\hbox{{\Updelta {}^34\tex g.,$$ f = \left( {{\frac{{{\raise0.7ex\hbox{${\Updelta {}^34\textO_2 }$} \!\mathord{\left/ {\vphantom {{\Updelta {}^34\textO_2 } {\left[ Selleck GSK1904529A {{}^34\textO_2 } \right]}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\left[ {{}^34\textO_2 } \right]}$}}}}{{{\raise0.7ex\hbox{${\Updelta {}^32\textO_2 }$} \!\mathord{\left/ {\vphantom {{\Updelta {}^32\textO_2 } {\left[ {{}^32\textO_2 } \right]}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\left[ {{}^32\textO_2 } \right]}$}}}}}} \right) \times 1000  (9)The key advantage of this technique is that discrimination

values can be derived in a matter of minutes (the time for a reaction) rather than days (the time for subsequent gas extraction and processing). This technique is in its infancy, but has been used already to study CO2 discrimination in Rubisco carboxylase reactions and O2 discrimination in mitochondrial terminal oxidases (McNevin et al. 2006; McNevin see more et al. 2007; Armstrong et al. 2008). Substrate water exchange in PSII Isotopic exchange of water-derived oxygen ligands of the oxygen-evolving complex (OEC) into O2 has been of long standing interest with PSII, because it contains information of how, when, and where substrate-water is bound to the OEC and in what manner it is oxidized to molecular O2—e.g. via: (1) a sequence of oxidation steps involving partial water oxidation mafosfamide intermediates; or (2) a concerted reaction mechanism during the S3 → S0 transition. A MIMS approach

to this question was first employed by Radmer and Selleck Rabusertib Ollinger (Radmer and Ollinger 1980a). They attempted to determine the rate of appearance of 18O in the O2 products of water splitting by PSII samples suspended in 18O-enriched water. The experiment is analogous to stop-flow experiments and requires rapid injection/mixing of isotopically labeled water into the suspension of photosynthetic samples followed by a series of light flashes to photogenerate O2. This first MIMS experiment indicates that water exchanges rapidly and by inference conceded that there are no non-exchangeable stable water oxidation products (e.g., bound peroxides) up to the S3 state of the OEC. This work and others that followed (Radmer and Ollinger 1980a, 1986; Bader et al. 1993) were limited by mixing/stabilization times of >30 s, and it wasn’t until more rapid mixing techniques were developed that also strongly reduced the O2 background rise from the injection of the labeled water that more specific information about water binding could be learned (Messinger et al. 1995).