Amino acid dating
Encyclopedia
Amino acid dating is a dating technique
used to estimate the age of a specimen in paleobiology
, archaeology
, forensic science, taphonomy
, sedimentary geology and other fields. This technique relates changes in amino acid
molecules to the time elapsed since they were formed.
s. All amino acids except glycine
(the simplest one) are optically active, having an asymmetric carbon
atom. This means that the amino acid can have two different configurations, "D" (dextrorotary) or "L" (laevorotary) which are mirror images of each other. With a few important exceptions, living organisms keep all their amino acids in the "L" configuration. When an organism dies, control over the configuration of the amino acids ceases, and the ratio of D to L moves from a value near 0 towards an equilibrium value near 1, a process called racemization
. Thus, measuring the ratio of D to L in a sample enables one to estimate how long ago the specimen died.
), and other characteristics of the enclosing matrix
. Also, D/L concentration thresholds appear to occur as sudden decreases in the rate of racemization. These effects restrict amino acid chronologies to materials with known environmental histories and/or relative intercomparisons with other dating methods.
Temperature and humidity histories of microenvironments are being produced at ever increasing rates as technologies advance and technologists accumulate data. These are important for amino acid dating because racemization occurs much faster in warm, wet conditions compared to cold, dry conditions. 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. As a rule of thumb, sites with a mean annual temperature of 30°C have a maximum range of 200 ka and resolution of about 10 ka; sites at 10°C have a maximum age range of ~2 m.y., and resolution generally about 20% of the age; at -10°C the reaction has a maximum age of ~10 m.y., and a correspondingly coarser resolution.
Strong acidity and mild to strong alkalinity induce greatly increased racemization rates. Generally, they are not assumed to have a great impact in the natural environment, though tephrochronological
data may shed new light on this variable.
The enclosing matrix is probably the most difficult variable in amino acid dating. This includes racemization rate variation among species and organs, and is affected by the depth of decomposition, porosity, and catalytic effects of local metals and minerals.
(A/I or D/L ratio). This amino acid ratio has the advantages of being relatively easy to measure and being chronologically useful through the Quaternary
.
Reverse phase HPLC techniques can measure up to 9 amino acids useful in geochronology over different time scales on a single chromatogram (Aspartic acid
, Glutamic acid
, Serine
, Alanine
, Arginine
, Tyrosine
, Valine
, Phenylalanine
, Leucine
).
In recent years there have been successful efforts to examine intra-crystalline amino acids separately as they have been shown to improve results in some cases.
, oceanography
, paleogeography, paleobiology
, and paleoclimatology
have been particularly affected. Their applications include dating correlation, relative dating, sedimentation rate analysis, sediment transport studies, conservation paleobiology, taphonomy
and time-averaging, sea level determinations, and thermal history reconstructions.
Paleobiology
and archaeology
have also been strongly affected. Bone, shell, and sediment studies have contributed much to the paleontological record, including that relating to hominoids. Verification of radiocarbon and other dating techniques by amino acid racemization and vice versa has occurred. The 'filling in' of large probability ranges, such as with radiocarbon reservoir effects, has sometimes been possible. Paleopathology and dietary selection, paleozoogeography and indigineity, taxonomy
and taphonomy
, and DNA viability studies abound. The differentiation of cooked from uncooked bone, shell, and residue is sometimes possible. Human cultural changes and their effects on local ecologies have been assessed using this technique.
The slight reduction in this repair capability during aging is important to studies of longevity and old age tissue breakdown disorders, and allows the determination of age of living animals.
Amino acid racemization also has a role in tissue and protein degradation studies, particularly useful in developing museum preservation methods. These have produced models of protein adhesive and other biopolymer deteriorations and the concurrent pore system development.
Forensic science can use this technique to estimate the age of a cadaver or an objet d'art to determine authenticity.
product can be combined with a chiral specific fluorescent, separated by chromatography
or electrophoresis
, and the particular amino acid D:L ratio determined by fluorescence. Alternatively, the particular amino acid can be separated by chromatography or electrophoresis, combined with a metal cation, and the D:L ratio determined by mass spectrometry
. Chromatographic and electrophoretic separation of proteins and amino acids is dependent upon molecular size, which generally corresponds to molecular weight, and to a lesser extent upon shape and charge.
Dating methodology (archaeology)
Dating material drawn from the archaeological record can be made by a direct study of an artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts...
used to estimate the age of a specimen in paleobiology
Paleobiology
Paleobiology is a growing and comparatively new discipline which combines the methods and findings of the natural science biology with the methods and findings of the earth science paleontology...
, archaeology
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
, forensic science, taphonomy
Taphonomy
Taphonomy is the study of decaying organisms over time and how they become fossilized . The term taphonomy was introduced to paleontology in 1940 by Russian scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms, from the biosphere, to the...
, sedimentary geology and other fields. This technique relates changes in amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
molecules to the time elapsed since they were formed.
Principle
All biological tissues contain amino acidAmino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s. All amino acids except glycine
Glycine
Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...
(the simplest one) are optically active, having an asymmetric carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atom. This means that the amino acid can have two different configurations, "D" (dextrorotary) or "L" (laevorotary) which are mirror images of each other. With a few important exceptions, living organisms keep all their amino acids in the "L" configuration. When an organism dies, control over the configuration of the amino acids ceases, and the ratio of D to L moves from a value near 0 towards an equilibrium value near 1, a process called racemization
Racemization
In chemistry, racemization refers to the converting of an enantiomerically pure mixture into a mixture where more than one of the enantiomers are present...
. Thus, measuring the ratio of D to L in a sample enables one to estimate how long ago the specimen died.
Factors affecting racemization
The rate at which racemization proceeds depends on the type of amino acid and on the average temperature, humidity, acidity (pHPH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
), and other characteristics of the enclosing matrix
Matrix (geology)
The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...
. Also, D/L concentration thresholds appear to occur as sudden decreases in the rate of racemization. These effects restrict amino acid chronologies to materials with known environmental histories and/or relative intercomparisons with other dating methods.
Temperature and humidity histories of microenvironments are being produced at ever increasing rates as technologies advance and technologists accumulate data. These are important for amino acid dating because racemization occurs much faster in warm, wet conditions compared to cold, dry conditions. 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. As a rule of thumb, sites with a mean annual temperature of 30°C have a maximum range of 200 ka and resolution of about 10 ka; sites at 10°C have a maximum age range of ~2 m.y., and resolution generally about 20% of the age; at -10°C the reaction has a maximum age of ~10 m.y., and a correspondingly coarser resolution.
Strong acidity and mild to strong alkalinity induce greatly increased racemization rates. Generally, they are not assumed to have a great impact in the natural environment, though tephrochronological
Tephrochronology
250px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at the height of the [[volcanologists]] hands is [[rhyolitic]] [[tephra]] from [[Hekla]]....
data may shed new light on this variable.
The enclosing matrix is probably the most difficult variable in amino acid dating. This includes racemization rate variation among species and organs, and is affected by the depth of decomposition, porosity, and catalytic effects of local metals and minerals.
Amino acids used
Conventional racemization analysis tends to report a D-allosioleucine / L-isoleucineIsoleucine
Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested. Its codons are AUU, AUC and AUA....
(A/I or D/L ratio). This amino acid ratio has the advantages of being relatively easy to measure and being chronologically useful through the Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
.
Reverse phase HPLC techniques can measure up to 9 amino acids useful in geochronology over different time scales on a single chromatogram (Aspartic acid
Aspartic acid
Aspartic acid is an α-amino acid with the chemical formula HOOCCHCH2COOH. The carboxylate anion, salt, or ester of aspartic acid is known as aspartate. The L-isomer of aspartate is one of the 20 proteinogenic amino acids, i.e., the building blocks of proteins...
, Glutamic acid
Glutamic acid
Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates...
, Serine
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
, Alanine
Alanine
Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...
, Arginine
Arginine
Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. At the level of molecular genetics, in the structure of the messenger ribonucleic acid mRNA, CGU, CGC, CGA, CGG, AGA, and AGG, are the triplets of nucleotide bases or codons that codify for arginine during...
, Tyrosine
Tyrosine
Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
, Valine
Valine
Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...
, Phenylalanine
Phenylalanine
Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...
, Leucine
Leucine
Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins...
).
In recent years there have been successful efforts to examine intra-crystalline amino acids separately as they have been shown to improve results in some cases.
Applications
Data from the geochronological analysis of amino acid racemization has been building for thirty-five years. Archeology, StratigraphyStratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
, oceanography
Oceanography
Oceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
, paleogeography, paleobiology
Paleobiology
Paleobiology is a growing and comparatively new discipline which combines the methods and findings of the natural science biology with the methods and findings of the earth science paleontology...
, and paleoclimatology
Paleoclimatology
Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...
have been particularly affected. Their applications include dating correlation, relative dating, sedimentation rate analysis, sediment transport studies, conservation paleobiology, taphonomy
Taphonomy
Taphonomy is the study of decaying organisms over time and how they become fossilized . The term taphonomy was introduced to paleontology in 1940 by Russian scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms, from the biosphere, to the...
and time-averaging, sea level determinations, and thermal history reconstructions.
Paleobiology
Paleobiology
Paleobiology is a growing and comparatively new discipline which combines the methods and findings of the natural science biology with the methods and findings of the earth science paleontology...
and archaeology
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
have also been strongly affected. Bone, shell, and sediment studies have contributed much to the paleontological record, including that relating to hominoids. Verification of radiocarbon and other dating techniques by amino acid racemization and vice versa has occurred. The 'filling in' of large probability ranges, such as with radiocarbon reservoir effects, has sometimes been possible. Paleopathology and dietary selection, paleozoogeography and indigineity, taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
and taphonomy
Taphonomy
Taphonomy is the study of decaying organisms over time and how they become fossilized . The term taphonomy was introduced to paleontology in 1940 by Russian scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms, from the biosphere, to the...
, and DNA viability studies abound. The differentiation of cooked from uncooked bone, shell, and residue is sometimes possible. Human cultural changes and their effects on local ecologies have been assessed using this technique.
The slight reduction in this repair capability during aging is important to studies of longevity and old age tissue breakdown disorders, and allows the determination of age of living animals.
Amino acid racemization also has a role in tissue and protein degradation studies, particularly useful in developing museum preservation methods. These have produced models of protein adhesive and other biopolymer deteriorations and the concurrent pore system development.
Forensic science can use this technique to estimate the age of a cadaver or an objet d'art to determine authenticity.
Procedure
Amino acid racemization analysis consists of sample preparation, isolation of the amino acid wanted, and measure of its D:L ratio. Sample preparation entails the identification, raw extraction, and separation of proteins into their constituent amino acids, typically by grinding followed by acid hydrolysis. The amino acid derivative hydrolysisHydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
product can be combined with a chiral specific fluorescent, separated by chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
or electrophoresis
Electrophoresis
Electrophoresis, also called cataphoresis, is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. This electrokinetic phenomenon was observed for the first time in 1807 by Reuss , who noticed that the application of a constant electric...
, and the particular amino acid D:L ratio determined by fluorescence. Alternatively, the particular amino acid can be separated by chromatography or electrophoresis, combined with a metal cation, and the D:L ratio determined by mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
. Chromatographic and electrophoretic separation of proteins and amino acids is dependent upon molecular size, which generally corresponds to molecular weight, and to a lesser extent upon shape and charge.
External links
- Fundamentals of sample age determination from its amino acid racemization by Policarp Hortolà
- Brown 1985 Amino Acid Dating. Origins 12(1):8-25
Active Laboratories
- Northern Arizona University Amino Acid Geochronology Laboratory
- University of Massachusetts Amino Acid Geochronology Laboratory
- The University of Colorado Amino Acid Geochronology Lab
- University of Delaware Research Group
- University of York BioArCh
- Madrid School of Mines Biomolecular Stratigraphy Laboratory