Racemization of isoleucine in calcareous marine sediments: Kinetics and mechanism

Bada, Jeffrey L.; Schroeder, Roy A.

doi:10.1016/0012-821x(72)90022-2

Cited by 140 publications

(82 citation statements)

References 13 publications

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“…Recent studies have shown that the reaction can be used to date deepsea sediments (4)(5)(6) and fossil bones (7)(8)(9). Because of the much slower reaction rate, the racemization reaction can be used to date fossil materials too old for radiocarbon dating.…”

mentioning

confidence: 99%

Concordance of Collagen-Based Radiocarbon and Aspartic-Acid Racemization Ages

Bada

Schroeder

Protsch

et al. 1974

Proc. Natl. Acad. Sci. U.S.A.

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By determining the extent of racemization of aspartic acid in a well-dated bone, it is possible to calculate the in situ first-order rate constant for the interconversion of the L and D enantiomers of aspartic acid. Collagen-based radiocarbon-dated bones are shown to be suitable samples for use in "calibrating" the racemization reaction. Once the aspartic-acid racemization reaction has been "calibrated" for a site, the reaction can be used to date other bones from the deposit. Ages deduced by this method are in good agreement with radiocarbon ages. These results provide evidence that the aspartic-acid racemization reaction is an important chronological tool for dating bones either too old or too small for radiocarbon dating. As an example of the potential application of the technique for dating fossil man, a piece of Rhodesian Man from Broken Hill, Zambia, was analyzed and tentatively assigned an age of about 110,000 years.The amino acids commonly found in living organisms consist mainly of the L-isomers. However, fossil materials have been found to contain D-amino acids, and the proportion of Damino acids to L-amino acids increases with the age of the fossil (1-9). The reaction responsible for this conversion is termed racemization. Each amino acid (with the exception of glycine) undergoes this process, some much faster than others. For example, in bone the racemization half-life (time required for D: L ratio to reach 0.333) at 200 for aspartic acid is about 15,000 years (9); at the same temperature the reaction for isoleucine has a half-life in excess of 100,000 years (8).The amino-acid racemization reaction has important applications in anthropology and geochronology. Recent studies have shown that the reaction can be used to date deepsea sediments (4-6) and fossil bones (7-9). Because of the much slower reaction rate, the racemization reaction can be used to date fossil materials too old for radiocarbon dating. Unfortunately, one limitation of this method is that the racemization reaction is temperature dependent. Thus, in order to date materials using the degree of racemization, some estimate of the temperature history of the region where the fossil was found must be available.Recently it has been shown (9) that by determining the extent of racemization of aspartic acid in a bone which has been dated by radiocarbon it is possible to calculate the in situ first-order rate constant for interconversion of the L-isomers and D-isomers of aspartic acid. Once this "calibration" has been carried out for a site, the racemization reaction can be used to date other bones from the area which are either too old or too small for radiocarbon dating. This "calibration" procedure eliminates the need for evaluating the temperature history of a bone before it can be dated using the amino-acid racemization reaction. The only assumption required, in using this approach, is that the average temperature experienced by the "calibration" sample is representative of the average temperature experienced by other samples from t...

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confidence: 99%

Concordance of Collagen-Based Radiocarbon and Aspartic-Acid Racemization Ages

Bada

Schroeder

Protsch

et al. 1974

Proc. Natl. Acad. Sci. U.S.A.

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“…A first-order kinetic model, expressed by the following equation, derived by Bada and Schroeder (1972) has been used to interpret the data:…”

Section: Methodsmentioning

confidence: 99%

“…Lisoleucine from protein undergoes an interconversion (epimerization) to yield D-alloisleucine. The extent of epimerization is used within certain limitations to estimate the age of the sediment (Bada et al, 1970;Wehmiller and Hare, 1971;Bada and Schroeder, 1972). Studies utilizing DSDP samples have considered the epimerization (usually called racemization) of isoleucine in sediment samples from Leg 15 (Hare, 1973;Bada and Man, 1973), Leg 37 (Bada et al, 1977), Leg 42A (Bada et al, 1978a), and Leg 42B (Mopper et al, 1978).…”

Section: Introductionmentioning

confidence: 99%

Amino Acids in Sediments from Leg 68 Site 502

Kvenvolden¹,

Blunt²

1982

Initial Reports of the Deep Sea Drilling Project

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“…Amino acids once entered into the sediments undergo a variety of chemical reactions to decrease their concentrations in the sediments with time. These decay reactions as well as the racemization reaction can be analyzed by a first-order reversible kinetic model (Bada et al, 1970;Wehmiller and Hare, 1971;Bada and Schroeder, 1972).…”

Section: Proteinaceousmentioning

confidence: 99%