An important discovery has been made with respect to the mystery of 鈥渉andedness鈥� in biomolecules. Researchers led by Sandra Pizzarello, a research professor at Arizona State University, found that some of the possible abiotic precursors to the origin of life on Earth have been shown to carry 鈥渉andedness鈥� in a larger number than previously thought.

The work is being published in this week鈥檚 Early Edition of the Proceedings of the National Academy of Sciences. The paper is titled, 鈥淢olecular asymmetry in extraterrestrial chemistry: Insights from a pristine meteorite,鈥� and is co-authored by Pizzarello and Yongsong Huang and Marcelo Alexandre, of Brown University.

Pizzarello, in ASU鈥檚 Department of Chemistry and Biochemistry, worked with Huang and Alexandre in studying the organic materials of a special group of meteorites that contain among a variety of compounds, amino acids that have identical counterparts in terrestrial biomolecules. These meteorites are fragments of asteroids that are about the same age as the solar system (roughly 4.5 billion years.)

Scientists have long known that most compounds in living things exist in mirror-image forms. The two forms are like hands; one is a mirror reflection of the other. They are different, cannot be superimposed, yet identical in their parts.

When scientists synthesize these molecules in the laboratory, half of a sample turns out to be 鈥渓eft-handed鈥� and the other half 鈥渞ight-handed.鈥� But amino acids, which are the building blocks of terrestrial proteins, are all 鈥渓eft-handed,鈥� while the sugars of DNA and RNA are 鈥渞ight-handed.鈥� The mystery as to why this is the case, 鈥減arallels in many of its queries those that surround the origin of life,鈥� said Pizzarello.

Years ago Pizzarello and ASU professor emeritus John Cronin analyzed amino acids from the Murchison meteorite (which landed in Australia in 1969) that were unknown on Earth, hence solving the problem of any contamination. They discovered a preponderance of 鈥渓eft-handed鈥� amino acids over their 鈥渞ight-handed鈥� form.

鈥淭he findings of Cronin and Pizzarello are probably the first demonstration that there may be natural processes in the cosmos that generate a preferred amino acid handedness,鈥� Jeffrey Bada of the Scripps Institution of Oceanography, La Jolla, Calif., said at the time.

The new PNAS work was made possible by the finding in Antarctica of an exceptionally pristine meteorite. Antarctic ices are good 鈥渃urators鈥� of meteorites. After a meteorite falls -- and meteorites have been falling throughout the history of Earth -- it is quickly covered by snow and buried in the ice. Because these ices are in constant motion, when they come to a mountain, they will flow over the hill and bring meteorites to the surface.

鈥淭hanks to the pristine nature of this meteorite, we were able to demonstrate that other extraterrestrial amino acids carry the left-handed excesses in meteorites and, above all, that these excesses appear to signify that their precursor molecules, the aldehydes, also carried such excesses,鈥� Pizzarello said. 鈥淚n other words, a molecular trait that defines life seems to have broader distribution as well as a long cosmic lineage.鈥�

鈥淭his study may provide an important clue to the origin of molecular asymmetry,鈥� added Brown associate professor and co-author Huang.

Source: Arizona State University