title: Bicarbonate, not CO2, is the species required for the stimulation of Photosystem II electron transport.
abstract: Evidence is presented that the bicarbonate ion (HCO3-), not CO2, H2CO3 or CO32-, is the species that stimulates electron transport in Photosystem II from spinach (Spinacia oleracea). Advantage was taken of the pH dependence of the ratio of HCO3- to CO2 at equilibrium in order to vary effectively the concentration of one species while holding the other constant. The Hill reaction was stimulated in direct proportion with the equilibrium HCO3- concentration, but it was independent of the equilibrium CO2 concentration. The other two carbonic species, H2CO3 and CO32-, are also shown to have no direct involvement. It is suggested that HCO3- is the species which binds to the effector site.
mesh_terms: D015086:2,6-Dichloroindophenol / Q000378:metabolism; D001639:Bicarbonates / Q000502:physiology*; D004579:Electron Transport; D010084:Oxidation-Reduction; D010788:Photosynthesis; D010944:Plants
chemical_list: D001639:Bicarbonates; D015086:2,6-Dichloroindophenol