Racemization Rates Of Amino Acids Research Articles

Amino acid racemization in four species of ostracodes: Taxonomic, environmental, and microstructural controls

Here we quantified the aspartic acid and glutamic acid racemization rates of the four main ostracode species (Herpetocypris reptans, Candona neglecta, Ilyocypris gibba and Cyprideis torosa) present in several Iberian Peninsula localities covering a wide chronological range (ca. 1 Ma to present). At low D/L values (at Asp D/L < 0.40; and Glu D/L = 0.09–0.18), H. reptans racemized at higher rates than C. neglecta, C. torosa and I. gibba. In contrast, for Asp D/L > 0.4 and Glu D/L > 0.18, H. reptans, C. neglecta and C. torosa showed similar racemization rates. I. gibba exhibited the lowest D/L values in old samples (Middle and Lower Pleistocene). We attribute these differences in amino acid racemization rates mainly to variations in valve protein composition. We found that the microstructure of the valves of each species (size, morphology, and arrangement of crystals) differed, but did not appear to change over time (at least for the last ca. 1 Ma). Such differences may also be linked to the type of proteins involved in the respective calcification processes of these organisms. On the basis of our results, and given that other studies have demonstrated that the majority of inter-crystalline proteins are leached early after death (a few centuries or millennia), we propose that the degradation rates of the most resistant inter- and intra-crystalline proteins in each species differ depending on the protein composition of the valves. Although further research is required, we suggest that amino acid racemization in each ostracode species might be related to valve microstructure.

Amino acid racemization rates in different genera of ostracodes

Ostracod shells from the archaeological site Gesher Benot Ya'aqov (GBY) in the upper Jordan River Valley (Israel) were investigated to improve the understanding of the environmental conditions of the Acheulian occupation site during the early-mid Pleistocene transition (0.78 Ma). The diverse ostracod assemblage consists of 28 species. The distribution of most of the recorded species in the region today shows that the hydrological conditions at the early-mid Pleistocene transition were not fundamentally different from the modern ones. However, the predominance of Candona neglecta shells in the GBY sequence probably indicates cooler climatic conditions than today. Shells of Candona angulata in the artefact-richer upper half of the sequence suggest a slight salinity increase in the ancient Hula Lake from pure freshwater to slightly oligohaline conditions. This shift probably resulted from wetter conditions and a more stable lake environment with increased residence time of the lake water and stronger influence of evaporation. Shells of the brackish water ostracod Cyprideis torosa and the slightly halophilic Heterocypris salina and Plesiocypridopsis newtoni were recorded only rarely suggesting that the lake maintained an outlet through the entire period represented by the GBY sequence. Shells of Gomphocythere ortali in GBY cycles 1 and 2 imply that a permanent freshwater stream existed close to the site. Humphcypris subterranea shells in cycles 3–5 provide further evidence that a tributary entered the lake from the south in contrast to the modern setting with the north–south flowing Jordan River at GBY. Statistical analysis of the quantitative ostracod data from GBY identified a group of samples from layers containing more abundant stone artefacts and another group of samples from layers with scarce artefacts. Samples from layers containing more abundant artefacts have relatively high abundances of C. angulata, Darwinula stevensoni and Physocypria kraepelini shells and include rare shells of Ilyocypris hartmanni, Ilyocypris salebrosa, Heterocypris incongruens and Pseudocandona sp. 2 which do not occur in the other samples. The presence of P. kraepelini and H. incongruens shells in artefact-richer sediments possibly indicates poor bottom water oxygenation in the ancient Hula Lake sometimes during the periods of Acheulian occupation. However, more detailed studies are required to assess whether lower dissolved oxygen levels in the lake resulted from a slight lake level rise and possibly higher nutrient flux to the lake during wetter conditions or whether hominins already impacted lake's nutrient status by butchering at its shore or by burning of near-shore vegetation.

Dating Silk By Capillary Electrophoresis Mass Spectrometry

A new capillary electrophoresis mass spectrometry (CE-MS) technique is introduced for age estimation of silk textiles based on amino acid racemization rates. With an L to D conversion half-life of ~2500 years for silk (B. mori) aspartic acid, the technique is capable of dating silk textiles ranging in age from several decades to a few-thousand-years-old. Analysis required only ~100 μg or less of silk fiber. Except for a 2 h acid hydrolysis at 110 °C, no other sample preparation is required. The CE-MS analysis takes ~20 min, consumes only nanoliters of the amino acid mixture, and provides both amino acid composition profiles and D/L ratios for ~11 amino acids.

Biomolecules in fossil remains: Multidisciplinary approach to endurance

Svante Pääbo, a leading pioneer in the study of ancient DNA, eloquently described the recovery of genetic information from the fossil record as a 21st Century form of genetic time travel1. The advent of PCR made possible the amplification of small amounts of DNA from fossil samples and allowed the direct study of phylogenetics from extinct organisms. Prior to this development, phylogenetic relationships determined by genetic variation relied mostly upon sequences from living organisms. The concept of time travel, via the analysis of ancient biomolecules, can be broadened to encompass numerous types of biomolecular information recovered from ancient bones. For example, palaeodiets and palaeoclimates can be reconstructed from stable isotopes of bone collagen, and estimations of age are obtained from amino acid racemization rates.

Amino acid abundances and stereochemistry in hydrothermally altered sediments from the Juan de Fuca Ridge, northeastern Pacific Ocean

The Juan de Fuca Ridge is a hydrothermally active, sediment covered, spreading ridge situated a few hundred kilometres off the west coast of North America in the northeastern Pacific Ocean. Sediments from seven sites drilled during the Ocean Drilling Program (ODP) Legs 139 and 168 were analyzed for total hydrolyzable amino acids (THAA), individual amino acid distributions, total organic C (TOC) and total N (TN) contents. The aim was to evaluate the effects of hydrothermal stress on the decomposition and transformation of sedimentary amino acids. Hydrolyzable amino acids account for up to 3.3% of the total organic C content and up to 12% of the total N content of the upper sediments. The total amounts of amino acids decrease significantly with depth in all drilled holes. This trend is particularly pronounced in holes with a thermal gradient of around 0.6°C/m or higher. The most abundant amino acids in shallow sediments are glycine, alanine, lysine, glutamic acid, valine and histidine. The changes in amino acid distributions in low temperature holes are characterized by increased relative abundances of non-protein β-alanine and γ-aminobutyric acid. In high temperature holes the amino acid compositions are characterized by high abundances of glycine, alanine, serine, ornithine and histidine at depth. D/L ratios of samples with amino acid distributions similar to those found in acid hydrolysates of kerogen, indicate that racemization rates of amino acids bound by condensation reactions may be diminished.

Estimation of Age from Teeth by Amino Acid Racemization: Influence of Fixative

To determine the age of a subject from teeth accurately utilizing the racemization rates of amino acids, standard samples of the same tooth species from the same jaw are necessary as controls, as well as data for identification. However, standard teeth are generally stored in fixatives such as ethanol and formalin. We investigated and compared the degree of progression of racemization of dentinal aspartic acid in teeth stored in 95% ethanol, 10% formalin, or 10% neutral formalin fixatives. The racemization rate of dentinal aspartic acid in teeth stored in 10% neutral formalin was the highest, followed by that for teeth stored in 10% formalin then that for teeth stored in 95% ethanol. Teeth stored in these fixatives at 15 degrees C showed almost no progression of racemization. The racemization ratio (D/L ratio) in teeth extracted 10 years previously was almost unchanged from that at the time of extraction, and allowed an accurate evaluation of the subjects age at tooth extraction.

Racemization rates of amino acids for dating ancient samples

Racemization rates of amino acids for dating ancient samples

Retardation of racemization rates of amino acids incorporated into melanoidins

Diagenetic reactions that affect the racemization of amino acids in fossils include hydrolysis of the original proteinaceous component and condensation of amino acids into “humic-like” materials. In this study, the consequences of condensation reactions for amino acid racemization rates are addressed. Aqueous solutions consisting of L-amino acids and D-glucose were heated ( 100°C) for up to 231 days. A comparison of racemization rates for amino acids in these solutions and in the resultant insoluble melanoidins indicates that the incorporation of amino acids into melanoidins retards racemization. In a sense, this retardation mimics the effect that has previously been attributed to the hydrolysis of proteinaceous material. An appraisal of the various diagenetic processes that may affect amino acid racemization rates in older fossil materials is essential for the refinement of geochemical research strategies that are dependent on this reaction.

Electronic spectral studies of nickel(II) alanine complexes

The electronic absorption spectrum of hydrated nickel(II) exhibits three bands, a broad band λ max at 658 nm and two sharp bands with λ max at 394 and 302 nm. The electronic absorption spectrum of Ni(II) and D- and L-alanine in aqueous solution shows the same three characteristic bands, but with λ max at 618,370 and 302 nm, with the absorption intensities increased for the first two bands. The three bands are assigned to the three spin-allowed d-d transitions 3A 2g → 3T 2g, 3A 2g → 3T 1g(F) and 3A 2g → 3T 1g(P) of octahedral nickel(II). Information about the Ni(II) complex formation mechanism and nature of the products was obtained from isosbestic points and pH profile studies of electronic spectra and amino acid racemization rates.

Racemization rates of 3,4-didehydro-2-amino acids

The racemization rates of amino acids in acidic medium (acetic acid) were studied. The sensitivity to racemization decreases in the order (E)-3,4-didehydroornithine &gt; (E)-Nδ-Z-3,4-didehydroornithine &gt;&gt; (Z)-3,4-didehydronorvaline &gt; ornithine, norvaline. (E)-3,4-Didehydroornithine is also relatively rapidly racemized on heating with 5 M or 0.05 M-HCl (100 °C).

ChemInform Abstract: Selective Racemization of Amino Acid Amides in the Presence of Amino Acids.

The significant differences in the racemization rates of amino acids and the corresponding amides make it possible to carry out selective racemization of amides in the presence of optically active amino acids.

Selective racemization of amino acid amides in the presence of amino acids

The significant differences in the racemization rates of amino acids and the corresponding amides make it possible to carry out selective racemization of amides in the presence of optically active amino acids.

Fraction dependent variation of aspartic acid racemization age of fossil bone

The extent of racemization of amino acids provides valuable information on the chronology of various fossil materials1–3. In bone, aspartic acid has received the most attention, and the D/L ratio of this amino acid has been used to estimate ages of human skeletal remains4–9. These estimates were, however, based on the degree of racemization determined for total remnant aspartic acid which may exist in various forms (that is, protein, peptide and free amino acid). The effect of the chemical state of amino acids on amino acid racemization rates or ages in calcareous marine sediments10 and shells11 has been discussed. In bones, the non-dialysable material in a heated modern sample has a lower racemization rate (isoleucine) than the total organic matrix12; free amino acids in fossil bone are more highly racemized than are bound (HCl-insoluble) amino acids13. The present investigation was designed to assess such fluctuation of aspartic acid racemization age for a given bone specimen as caused by the variability of the form in which the amino acid is present.

Amino acid racemization dating of fossil bones

Abstract The development of amino acid racemization as a dating technique holds considerable promise for resolving questions of human evolution and culture histories. The advantages of this method are: fossil bone can be directly dated; only gram quantities are needed for analysis; and the range extends beyond that of radiocarbon. Amino acid racemization rates are dependent upon both time and temperature. In order to eliminate the need for evaluating the temperature history of a bone before it can be dated by racemization, a procedure has been developed wherein the in situ racemization rate is determined from the extent of racemization in a radiocarbon‐dated bone. Once this ‘calibration’ has been completed for a particular site, other bones from the area can be dated. Racemization ages deduced using this procedure are shown to be in close agreement with radiocarbon dates. The effects which other physical factors (pH, humidity, leaching) have on racemization rates are discussed. Because of the close correl...

Racemization of Amino Acids in Bones

IT has been shown that the extent of racemization of amino acids in a fossil can be used with certain limitations to estimate the age of the specimen1–6. For this dating work it is necessary to understand the kinetics and mechanism of the reactions involved. Here we show, by kinetic studies using modern bovine bone fragments heated in sealed ampoules for various time periods at several elevated temperatures, that the order of racemization rates of amino acids in bone is aspartic acid>alanine=glutamic acid>isoleucine≅leucine. Fossil bones not contaminated with modern amino acids are shown to have the same sequence of racemization rates.