From “New Light Shone On Photosynthesis” (ScienceDaily, Apr. 3, 2012), we learn, re photosynthesis,
On illumination, two water molecules bound at the cluster are split into molecular oxygen and four protons. Since water molecules are very stable, this process requires that the metal cluster be capable of efficiently performing very energetic reactions.
Allen, Williams and coworkers are trying to understand how a primitive anoxygenic organism that was capable of performing only simple low energy reactions could have evolved into oxygen-producing photosynthesis.
They have been manipulating the reaction center of the purple bacterium Rhodobacter sphaeroides encouraging it to acquire the functions of photosystem II. In the recent publication, they describe how a mononuclear manganese bound to the reaction center has gained some of the functional features of the metal cluster of photosystem II.
Although the mononuclear manganese cannot split water, it can react with reactive oxygen species to produce molecular oxygen. These results suggest that the evolution of photosynthesis might well have proceeded through intermediates that were capable of oxygen production and served until a protein with a bound manganese-calcium cluster evolved.
The problem is, we have no way of knowing whether an intermediate would be useful (usually they are not, which is endgame), let alone how a protein with a bound manganese-calcium cluster evolved. All we know is that mononuclear manganese – manipulated by scientists – cannot split water but can react to produce oxygen.
It’s interesting, but we really need the lab notes of the scientists who were doing this on the early Earth.