Paul W. Krieger (pkrieger@emerald.tufts.edu) responds:

Consider the intricacy of design in the Oxygen-Emitting Complex (OEC) of photosystem II (PSII), responsible for oxidizing two water molecules to produce one dioxygen molecule (plus four protons) as a waste product that sustains all aerobic life. This system is found in all cells producing oxygen as a byproduct of photosynthesis.

The fascinating feature here is a system containing four manganese ions of varying oxidation states, held tightly together by di-mu-oxo bridges in a dimer-of-dimer geometric arrangement. It accepts precisely four photons from sunlight per catalytic cycle, transforming geometric shape with each impeding photon in a very elegant manner (adamantane-like geometry to cubane structure); while transforming water to molecular oxygen with an efficiency that puts industrial processes to shame; while supplying four electrons to photosystem I (PSI), wherein magnesium-based photopigments (eg, P680) are further excited by light to pass on a continuous supply of excited electrons to an intervening electron transport chain.

The OEC active site is a nanoscale atomic-level machine that transforms solar energy into the food we eat at the dinner table; whether plant, meat, poultry or fish. It is ultimately the main source of energy (in series with PSI) that *eventually* fuels our cars (ie, dead organic matter forms sub-terrestrial oils) so that we can drive to pick-up our own energy stores at market... as food. I can't wait to see how many Nobel prizes it will take to model this system effectively with any comparable degree of efficiency!!

The OEC component of PSII not only supplies the oxygen necessary to sustain the organisms that later consume it in a sophisticated interdependent ecological exchange, but simultaneously supplies the electron transport chain via PSI carrying *ALL* biologically-sustained chemical energy sourced from the sun!!! [consistently harnessed energy, manipulated to drive the chemistry of photosynthesis] The only logical, scientifically feasible explanation, is an intelligent process designed by a designer--with greater intelligence than the sum of all applied scientific knowledge.

"Challenging problems of this complexity require the collaborative interaction of a number of research groups bringing a wide range of expertise in order for significant progress to be made. Included are geneticists, photophysicists, theoretical chemists, biophysical chemists, inorganic chemists, biochemists, and synthetic model builders, all of whom contribute to the current excitement in bioinorganic chemistry research through their willingness to tackle such significant and interesting problems as the OEC." From: Lippard, S. J.; Berg, J. M. "Principles in Bioinorganic Chemistry" Univ. Sci. Books: CA, 1994, p. 389.

Remarkably, this system is one-of-a-kind (no known variations), exhibiting irreducible complexity at many levels!! How could any ecosystem demanding a continuous, balanced atmospheric-supply of oxygen survive without the OEC when no alternate intermediary forms (or any other functional example) have been portrayed? It seems at least equally difficult to set-up a biosystem capable of producing the oxygen (as a waste product?), never mind enzymatically breaking it down in a controlled manner!

______________________________________________________ Ó 2010 Arthur V. Chadwick, Ph.D.