The origin of life and the left-handed amino-acid excess: the furthest heavens and the deepest seas?
The origin of life is an extraordinary problem that leads back to the structure and dynamics of the cosmos and early development of organic molecules. Within that wider question lies an unsolved problem that has troubled biologists for 150 years. What is the origin of the dominant presence of left-handed stereoisomers of amino acids in nature even though their synthesis normally results in an equal mixture of the right- and left-handed molecular forms? We propose that asymmetric Earth rotation caused at dawn and dusk circularly polarized UV light (CPUVL) of opposite polarity and reversed temperature profiles in the oceans. Destruction of the d-isomer by CPUVL at dusk in a sea surface hotter than at dawn created a daily l-isomer excess protected from radiation by nightfall, preserved by down-flow (diffusive, mechanical) into cold, darker regions, eventually initiating an l-amino-acid excess embodied in early marine forms. Innumerable mechanisms have been proposed for the origin of l-chiral dominance in amino acids and none proven. Since the thalidomide tragedy, homochirality of amino acids has been a growing practical issue for medicine. Understanding its origin may bring further and unexpected benefits. It may also be a modest pointer to the possibility of positive answers to whether intelligent life will have the capacity to continue to protect itself from conditions inimical to survival.
Goodman
Geoffrey
G
Division of Rheumatology, Allergy and Clinical Immunology, University of California at Davis School of Medicine, 451 East Health Sciences Drive, Suite 6510, Davis, CA 95616, USA.
Gershwin
M Eric
ME
D000596:Amino Acids / Q000737:chemistry*; D005075:Biological Evolution; D018534:Earth, Planet; D005118:Extraterrestrial Environment; D009792:Oceans and Seas; D000069497:Origin of Life; D010777:Photochemistry; D019445:Solar Activity; D013237:Stereoisomerism
D000596:Amino Acids