Amino acid racemization dating
Racemization is the process in which one enantiomer of a compound, such as an L-amino acid, converts to the other enantiomer.The compound then alternates between each form while the ratio between the ( ) and () groups approaches 1:1, at which point it becomes optically inactive.Since ( ) and () are experimental parameters, the absolute configuration of atoms in chiral molecules are commonly described using R and S, from the Latin rectus (right-handed) and sinistrus (left-handed).An older convention, commonly used by biochemists to describe amino acids and sugars, uses the letters D and L to designate absolute configuration (Figure 1).(See box, Pasteurs Racemic Revelation.) In a laboratory setting, scientists are able to measure the degree of racemization using polarimetry, liquid chromatography, capillary electrophoresis, and mass spectrometry.
(To hear a radio interview with George, visit The only other animals with similarly long life spans are the giant tortoise and the giant clam, which some have claimed can live about 150 and 220 years, respectively.They needed scientific data, however, to prove the whales longevity.Researchers turned to Jeffrey Bada and his colleagues at the Scripps Institution of Oceanography in La Jolla, CA, who are considered experts in the field of racemization analysis.By conducting aspartic acid racemization measurements using an HPLC/fluorescence detection method, Bada analyzed the bowheads eye lenses to estimate the whales age at the time of death (2).The eye lens of a bowhead whale is made up of dozens of layers of protein, much like an onion.The first layer is completely formed while the animal is still in the womb, and then becomes biologically inactive (Figure 2). Similar to the rings on a tree trunk, the lens of a whales eye is composed of concentric spheres of protein, with the oldest rings nearest the center.Following the onset of inactivity, racemization of amino acids begins and can be measured to estimate the amount of time since the initial deposit of the layer. By measuring the degree of aspartate race mization at the centermost sphere, researchers estimate the age of dead whales. Once the L-form is incorporated, it begins to racemize.The longer the racemization process continues, the closer to 1 the ratio between the D- and L-forms becomes.This ratio allows chemists to approximate a birth date of a bowhead whale by estimating how long it has been since the first layer in the eye lens formed.Bada and his colleagues studied the eye lenses of 48 bowhead whale carcasses harvested between 19.The proteins in each lens nucleus were acid hydrolyzed into free amino acids, which were then derivatized.