Origins of life: keys to an early chemical.

Given the intricacy of life's molecular processes, questions surrounding the earliest biochemistry loom large. How, for instance, did life's key chemical components arise on Earth -- and in what order?

Addressing these questions, Anthony D. Keefe, Gerald L. Newton, and Stanley L. Miller, all chemists at the University of California, San Diego, describe in the Feb. 23 Nature, a possible pathway for the evolution of an important biological molecule. They report synthesizing, in conditions similar to those most likely present on early Earth, the molecule pantetheine.

Pantetheine forms a chunk of a larger molecule, coenzyme A. Because coenzyme A acts in conjunction with other enzymes to facilitate reactions in living organisms, the authors believe it may have "acted in this capacity very early in the development of life on Earth."

Among other things, coenzyme A helps amino acids hook together and aids in making peptides. Both functions may have supported early evolution of proteins and nucleic acids, such as RNA and DNA.

Moreover, the building blocks of coenzyme A "have been shown to be probable prebiotic compounds," the chemists observe. In their current experiment, they show that pantetheine can form at temperatures as low as 40o Celsius, in circumstances typical of evaporating bodies of water beside beaches and lagoons. "These results suggest that pantetheine could have been a component of the prebiotic soup," they say.

While stressing that "nobody knows the exact sequence of events that led to life," Miller adds that "this finding opens many questions." For instance, if coenzymes appeared before life, "they may have helped make certain chemical pathways more efficient. It's possible that coenzymes became involved in important reactions even before there were living organisms."

Had the building blocks of coenzyme A emerged independently near lakes or oceans, they could have been incorporated more easily into early self-replicating chemical systems or metabolic cycles, he adds.

"Coenzyme A looks like a prebiotic type of molecule because it seems to have formed from assorted building blocks, such as nucleotides and amino acids," says James P. Ferris, a chemist at Rensselaer Polytechnic Institute in Troy, N.Y. "You get the feeling the molecule formed in a mixing pot of prebiotic precursors."

Pointing out the versatility of coenzymes, Ferris adds that "they may have survived because they can do some tasks that neither nucleic acids nor proteins can do."

"This work is significant because it supports the idea that these component molecules may have been around on the early Earth, reacted together, and survived because they were useful to proteins and nucleic acids."

Indeed, Miller highlights the point that the reactions leading to pantetheine could occur at a mere 40oC, close to the temperature of a rocky surface on a July day. Miller now wants to search for other molecules that might have formed at the edge of a warm beach.