Abstract
Kelvin considered it unlikely that sufficient time had elapsed on the earth for life to have reached its present level of complexity. In the warm surroundings in which life first appeared, however, elevated temperatures would have reduced the kinetic barriers to reaction. Recent experiments disclose the profound extent to which very slow reactions are accelerated by elevated temperatures, collapsing the time that would have been required for early events in primordial chemistry before the advent of enzymes. If a primitive enzyme, like model catalysts and most modern enzymes, accelerated a reaction by lowering its enthalpy of activation, then the rate enhancement that it produced would have increased automatically as the environment cooled, quite apart from any improvements in catalytic activity that arose from mutation and natural selection. The chemical events responsible for spontaneous mutation are also highly sensitive to temperature, furnishing an independent mechanism for accelerating evolution.
Highlights
Enzymes allow certain reactions to take place take place rapidly as compared with other reactions that confer no selective benefit upon the host organism
To estimate the minimal binding affinity expected of an ideal transition state analogue inhibitor that perfectly resembles the altered substrate in the transition state, it is necessary to compare the rate of reaction of the enzymesubstrate complex with the rate of the uncatalyzed reaction in water
When the rate enhancements produced by pyridoxal phosphate (PLP) and CeIV were examined as a function of temperature, the effects of these powerful catalysts were found to be based entirely on the reduction of ⌬H‡, whereas their effects on T⌬S‡ were somewhat unfavorable [23]
Summary
Enzymes allow certain reactions to take place take place rapidly as compared with other reactions that confer no selective benefit upon the host organism. After the publication of The Origin of Species, William Thomson (Lord Kelvin) became interested in the age of the earth and set his students to measuring temperatures at various depths in the soil He used those results to calculate the rate of heat loss from the earth, assuming that the earth began as a molten mass, and estimated the age of the earth as between 20 and 40 million years. In Kelvin’s inaugural address as president of the British Association, he stated his conviction that insufficient time had elapsed on Earth for the chemistry of living systems to have attained its present level of complexity without “intelligent and benevolent design” [9] Had he been aware of the generation of heat by the radioactivity of the earth, a phenomenon that would only be discovered much later, Kelvin would not have underestimated the age of the earth ( known to be ϳ4.6 billion years) by a factor of ϳ100.
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