Heat helped hasten life’s beginnings

UNC CHAPEL HILL (US) — The time required for evolution on a warm earth is shorter than previously thought, according to new research investigating the effect of temperature on extremely slow chemical reactions.

Enzymes, proteins that jump-start chemical reactions, are essential to life within cells of the human body and throughout nature.

These molecules have gradually evolved to become more sophisticated and specific, says Richard Wolfenden, professor of biochemistry and biophysics at University of North Carolina at Chapel Hill.

The findings are published in the online early edition of the Proceedings of the National Academy of Sciences.

To appreciate how powerful modern enzymes are, and the process of how they evolved, scientists need to know how quickly reactions occur in their absence.

Wolfenden measured the speed of chemical reactions, estimating that some of them take more than 2 billion years without an enzyme.

In the process of measuring slow reaction rates, “it gradually dawned on us that the slowest reactions are also the most temperature-dependent,” Wolfenden says.

In general, the amount of influence temperature has on reaction speeds varies drastically. In one slow reaction, for instance, raising the temperature from 25 to 100 degrees Celsius increases the rate 10 million fold. “That is a shocker,” Wolfenden says. “That’s what’s going to surprise people most, as it did me.”

It’s surprising, Wolfenden says, because for more than a century, a textbook rule in chemistry has been that the influence of temperature is modest. In particular, a doubling in reaction rate occurs when the temperature rises 10 degree Celsius, according to experiments done in 1866.

High temperatures were probably a crucial influence on reaction rates when life began forming in hot springs and submarine vents, Wolfenden says. Later, the cooling of the earth provided selective pressure for primitive enzymes to evolve and become more sophisticated.

Using two different reaction catalysts—which are not protein enzymes but that may have resembled early precursors to enzymes—Wolfenden and colleagues put the hypothesis to the test. The catalyzed reactions are indeed far less sensitive to temperature, compared with reactions that are accelerated by catalysts. The results are consistent with the hypothesis, Wolfenden says.

The next step is to test the hypothesis using other catalysts. In the meantime, these findings are likely to influence how scientists think of the first primitive forms of life on earth, and may affect how researchers design and enhance the power of artificial catalysts, he added.

Support for the research came from the National Institute of General Medicine, a component of the National Institutes of Health.

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