Impact of temperature on the time required for the establishment of primordial biochemistry, and for the evolution of enzymes
Randy B. Stockbridge, Charles A. Lewis, Jr., Yang Yuan, and Richard Wolfenden1
-Author Affiliations
Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599
Contributed by Richard Wolfenden, September 29, 2010 (sent for review August 1, 2010)
Abstract
All reactions are accelerated by an increase in temperature, but the magnitude of that effect on very slow reactions does not seem to have been fully appreciated. The hydrolysis of polysaccharides, for example, is accelerated 190,000-fold when the temperature is raised from 25 to 100 °C, while the rate of hydrolysis of phosphate monoester dianions increases 10,300,000-fold. Moreover, the slowest reactions tend to be the most heat-sensitive. These tendencies collapse, by as many as five orders of magnitude, the time that would have been required for early chemical evolution in a warm environment. We propose, further, that if the catalytic effect of a “proto-enzyme”—like that of modern enzymes—were mainly enthalpic, then the resulting rate enhancement would have increased automatically as the environment became cooler. Several powerful nonenzymatic catalysts of very slow biological reactions, notably pyridoxal phosphate and the ceric ion, are shown to meet that criterion. Taken together, these findings greatly reduce the time that would have been required for early chemical evolution, countering the view that not enough time has passed for life to have evolved to its present level of complexity.
activation energy, thermophilic organisms, pyridoxal phosphate, phosphate ester hydrolysis, amino acid decarboxylation
Footnotes
1To whom correspondence should be addressed. E-mail:water@med.unc.edu.
Author contributions: R.W. designed research; R.B.S., C.A.L., and Y.Y. performed research; C.A.L., Y.Y., and R.W. analyzed data; and R.B.S. and R.W. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at
*In all known cases, Km values increase with increasing temperature. Thus, the ΔH‡-lowering effect of enzymes becomes even more striking if kcat/Km, rather than kcat, is used as a basis for comparison.
†The only known exception, the peptidyl transferase center of the ribosome, produces a relatively small rate enhancement (107-fold) that arises entirely from a more favorable TΔS‡. This entropic effect is believed to arise from physical desolvation and juxtraposition of the two substrates, rather than from chemical catalysis in the usual sense. The enthalpic barrier to uncatalyzed peptidyl transfer (ΔH‡ = 8 kcal/mol in water)—which is much smaller than those of the reactions considered here, actually increaseswithin the active site of the ribosome (49).
Freely available online through the PNAS open access option.
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