Although protein function is thought to depend on flexibility, precisely how the dynamics of the molecule and its environment contribute to catalytic mechanisms is unclear. We review experimental and computational work relating to enzyme dynamics and function, including the role of solvent. The evidence suggests that fast motions on the 100 ps timescale, and any motions coupled to these, are not required for enzyme function. Proteins where the function is electron transfer, proton tunneling, or ligand binding may have different dynamical dependencies from those for enzymes, and enzymes with large turnover numbers may have different dynamical dependencies from those that turn over more slowly. The timescale differences between the fastest anharmonic fluctuations and the barrier-crossing rate point to the need to develop methods to resolve the range of motions present in enzymes on different time- and lengthscales.

We propose that life emerged from growing aggregates of iron sulphide bubbles containing alkaline and highly reduced hydrothermal solution. These bubbles were inflated hydrostatically at sulphidic submarine hot springs sited some distance from oceanic spreading centers four billion years ago. The membrane enclosing the bubbles was precipitated in response to contact between the spring waters and the mildly oxidized, acidic and iron-bearing Hadean ocean water. As the gelatinous sulphide bubbles aged and were inflated beyond their strength they budded, producing contiguous daughter bubbles by the precipitation of new membrane.[FeeS2] +/0 or [Fe4S4 ]2+/+ clusters, possibly bonded by hydrothermal thiolate ligands as proferredoxins, could have catalyzed oxidation of thiolates to disulphides, thereby modifying membrane properties.We envisage the earliest iron sulphide bubbles (proCorrespondence to: M. J. Russell Glossary: Hollow pyrite botryoids: hollow hemispheres of cryptocrystalline pyrite (FeS2) 0.1-1 mm across. Fischer-Tropsch syntheses: the highly exothermic catalytic hydrogenation of CO to hydrocarbons and aliphatic oxygenated compounds using finely divided iron. Greigite (Fe3S4): metastable iron sulphide precipitated from aqueous solution in a gel at 100°C and containing two-thirds of its iron as the high-spin ferric ion. Haber-Bosch process: the exothermic catalytic hydrogenation of nitrogen to yield ammonia. Probotryoid: a hydrostatically inflated colloidal iron monosulphide bubble; precursor to hollow botryoids and the progenitor to protocelts. Proferredoxins: [F%S2] and [F%MS4] clusters (M = Fe, Mo, W, Ni, etc.) ligated by abiogenic thiols and thiolates. Protocell: a cell comprised mainly of abiogenic organics including thiols with subordinate iron sulphides, partly as proferredoxins; growth results from catabolism and osmotic pressure botryoids) first growing by hydrostatic inflation with hydrothermal fluid, but evolving to grow mainly by osmosis (the protocellular stage), driven by (1) catabolism of hydrothermal abiogenic organics trapped on the inner walls of the membrane, catalyzed by the iron sulphide clusters; and (2) cleavage of hydrophobic compounds dissolved in the membrane to hydrophilic moieties which were translocated, by the proton motive force inherent in the acidic Hadean ocean, to the alkaline interior of the protocell. The organics were generated first within the hydrothermal convective system feeding the hot springs operating in the oceanic crust and later in the pyritizing mound developing on the sea floor, as a consequence of the reduction of CO, CO e, and formaldehyde by Fe z+-and se--bearing minerals. We imagine the physicochemical interactions in and on the membrane to have been sufficiently complex to have engendered auto-and cross-catalytic replication. The membrane may have been constructed in such a way that a "successful" parent could have "informed" the daughters of membrane characteristics functional for the then-current level of evolution.

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