What is amino acid racemization?
Amino Acid Racemization (or AAR) is the process by which there is an interconversion of amino acids from one chiral form (the L - laevo amino acids which are the building blocks of proteins)
to a mixture of L- and D- (dextro) forms following protein degradation. At equilibrium there is typically a 1:1 ratio of L to D forms and this mixture is said to be racemic.
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Application to dating (Geochronology)
The increase in the proportion of D-amino acids (a function of time and temperature) can be used as a tool
for estimating age. Attempts to provide absolute dates calibrate the amount of racemization using samples of known age and then use these predict the age of samples with known D/L values but of unknown age.
A recent paper by Kaufman (in press Geology) estimates that the compound accuracy of this approach is +/- 20%
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Intra-crystalline amino acids
In most biominerals (but not all, bone is a notable exception) amino acids occur within the biomineral crystallites, where they modify the behavior of the biomaterial.
We use a simple approach, prolonged bleach treatment to remove any other amino acids (in the case of molluscs mainly silk-like protein from
the organic matrix in which the crystallites are embedded . At BIOARCH we are currently testing if this approach improves analytical precision.
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