Engine of life and big bang of evolution: a personal perspective

Abstract

Photosystem II (PS II) is the engine for essentially all life on our planet and its beginning 2.5 billion years ago was the 'big bang of evolution.' It produces reducing equivalents for making organic compounds on an enormous scale and at the same time provides us with an oxygenic atmosphere and protection against UV radiation (in the form of the ozone layer). In 1967, when I began my career in photosynthesis research, little was known about PS II. The Zscheme had been formulated [Hill and Bendall (1960) ' What a change in our level of understanding of PS II since then! The contributions of many talented scientists have unraveled the mechanisms and structural basis of PS II function and we are now very close to revealing the molecular details of the remarkable and thermodynamically demanding reaction which it catalyzes, namely the splitting of water into its elemental constituents. It has been a privilege to be involved in this journey.

The fast and slow kinetics of chlorophyll a fluorescence induction in plants, algae and cyanobacteria: a viewpoint

“…Other fluorescence quenching and fluorescence lowering effects that have been considered for the PS fluorescence decay, and more generally for the P(SM)T fluorescence decay, include the accumulation of P 680 + (Shinkarev and Govindjee 1993;Bruce et al 1997) and of Pheo - (Klimov et al 1985), energy dissipative PSET around PS II (review by Kramer et al 2004), efflux of Mg 2+ from the intrathylakoid space, as counterion for the incoming H + and the destacking of grana it causes (review by Barber 2004), constitutive quenching by Zx (Govindjee and Seufferfeld 2002) and transmembrane electric potential-induced shifts in the energy levels of photosynthetic pigment (Stark effect; Falkowski et al 2004). …”

“…Compared to the OP rise, which is the integrated response of excited Chls a to redox signals and electrostatic fields that PSET generates within the thylakoid membrane, the PS decay is manifestly far more complex (see reviews by Barber 1976Barber , 1982Barber , 2004Briantais et al 1986;Krause andWeis 1984, 1991;and Krause and Jahns 2004). For one thing, in addition to the intramembranous PSET signals, we must now take into account the coupled-to-PSET proton influx into the lumen and the host of global signals this generates, such as lumen acidity, transmembrane DpH and D[metal cation] (due to counterion transport), and transmembrane electric potential difference (Dw); and for a second, in contrast to the OP fluorescence rise, which even isolated membrane particles can display, the PS decay depends on the existence of an intact chloroplast envelope which ensures maintenance of necessary levels of stromal solutes (Krause 1974;Barber et al 1974).…”

The Structure of Photosystem II and the Mechanism of Water Oxidation in Photosynthesis

“…These reactions result in the conversion of light energy into biologically useful chemical energy and the evolution of molecular oxygen. Thus, photosynthetic water splitting is one of the most important biochemical reactions on earth (3,4).…”

Molecular Mechanisms of Photoadaptation of Photosystem I Supercomplex from an Evolutionary Cyanobacterial/Algal Intermediate

“…The emergence of oxygenic photosynthesis in cyanobacteria over 2.5 billion years ago is often dubbed the Big Bang of evolution (Barber, 2004), as it gave rise to an aerobic atmosphere and protective ozone layer and allowed efficient aerobic cellular respiration and the colonization of Earth's surface by metazoan life. As such, it triggered fundamental biosphere changes on an unprecedented scale.…”