In neutral solution in the absence of enzymes, some biological reactions proceed with half-lives exceeding the age of Earth; yet life is believed to have taken hold within the first 25% of Earth's history. How did cellular chemistry, and the enzymes that make life possible, get started so quickly? According to a conventional rule of thumb, the rates of most reactions double when the temperature is raised from 20 to 30 �C. Compounding that effect, the rates of reactions would be expected to increase by a factor of 70 when the temperature is raised from 25 to 100� C. Recent experiments at elevated temperatures have shown that slow reactions are much more steeply dependent on temperature than that rule would imply. Moreover, the slowest reactions tend to be most heat-sensitive. That tendency greatly reduces the time that would have been required for early chemical evolution in a hot environment. That tendency also, suggests some likely properties of an evolvable catalyst. If the effect of a primitive enzyme was to reduce a reaction's enthalpy of activation, then the resulting rate enhancement would have increased automatically as the environment cooled. The same is not true of a purely entropic catalyst. The rate enhancements produced by modern enzymes and by some plausible prebiotic catalysts of slow reactions prove to be entirely enthalpic in origin. These observations collapse the time that would seem to have been required for the appearance of primordial chemistry and the early evolution of enzymes.

Thermal collapse of the time required for primordial chemistry and the early evolution of enzymes

248th National Meeting (2014)

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