Such extrapolations have been fairly recently (1999) called into question by experiments showing that models based on high temperature kinetics fail to predict racemization kinetics at physiologic temperatures (i.e., 37 C). We argue that the D: L ratio of Asx reflects the proportion of non-helical to helical collagen "The local buffering effects of bone and shell matrixes are supposed to limit this effect, but it is still something to consider as potentially significant when acting over the course of tens of thousands to millions of years.replacement of the asparagine residue with aspartic acid resulted in a 34-fold decrease in the rate of succinimide (Asu) formation.
The authors of this particular paper went on to suggest that, "As conformation strongly influences the rate of Asu [cyclic succinimide] formation and hence Asx [aspartic acid asparagine] racemization, the use of extrapolation from high temperatures to estimate racemization kinetics of Asx in proteins below their denaturation temperature is called into question . In the position carboxyl to asparagine in the peptide the replacement of glycine with a bulky amino acid such as proline or leucine resulted in a 33-50-fold decrease in the rate of deamidation"Hydrolysis, or the process of breaking down a protein into smaller and smaller fragments, clearly affects the rate of racemization.
The long-term rate of racemization for amino acids preserved in fossil ostracode shells was determined by using independently dated sediment cores from five deep lakes.
The racemization rates for aspartic and glutamic acids in the common ostracode genus were calibrated for the past 100 k.y., providing the basis for an age equation with a realistic age uncertainty of ∼±20%.
Factors affecting racemization The rate at which racemization proceeds depends upon the type of amino acid, average temperature, humidity, acidity, alkalinity, and enclosing matrix.
Temperate to cold region studies are much more common than tropical studies, and the steady cold of the ocean floor or the dry interior of bones and shells have contributed most to the accumulation of racemization dating data.
Over the past 60 years, many researchers and laboratories around the world have been involved with the development of the method and its application to diverse environments.
Amino acid dating is a dating technique used to estimate the age of a specimen in paleobiology, archaeology, forensic science, and other fields.Its main weakness is the fact that it is a molecular- rather than an atomic-scale reaction (cf.radionuclide decay), and as a consequence the rate is sensitive to temperature.The rate at which racemization proceeds depends upon the type of amino acid, average temperature, humidity, acidity, p H, and characteristics of the enclosing matrix.Also, D/L concentration thresholds appear to occur as sudden decreases in the rate of racemization.