M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Dating - CSAPÓ János, KÖLTŐ László , PAP Ildikó: Archaeological age determination based on the racemization and epimerization of amino acids

In the shells from prehistoric times, as well as in bones and teeth, Abelson examined the amino acid content for the first time, and published his findings in 1954. The fossils examined by him, a fishbone originating from the Devonian Age, contained glycine, alanine, glutamic acid, leucine, valine and aspartic acid, despite its age of approximately 360 million years. In his laboratory experiments he found that these amino acids lasted the longest, and under favourable temperature conditions these could be expected to survive as long as several million years. In 1954 Abelson made the first proposal to use the decomposition of proteins in fossils for the determination of age. He was the first to suggest that some correlation might exist between the decomposition of protein and the assessment of temperature; i. e.he can be considered as the first forefather of geothermometry. Following the examination of the decomposition of amino acids, Vallentyne (1964) made a new proposal in the direction of géothermie methods. This was based on the selective decomposition of amino acids. Hare and Abelson reported in 1967 that the D-amino acids found in fossils probably originated from the decomposition of L-amino acids. By examining the composition of amino acids in fossils-shells of increasing age they found that the ratio of D-amino acids increases in relation to the L-amino acids as the age increases. In the examined fossils, which were of the Miocene age, the amino acids could be traced only in the form of raceme. Hare and Mitterer (1968) conducted experiments on the racemization of Lisoleucine at high temperatures. By applying the conclusions of their experiments on a fossil-shell, the ratio of D-alloisoleucine and L-isoleucine was found to be 032, which enabled them to estimate the age at 70000 years. This was the first application of racemization (or in this case rather epimerization) in geochronology

. Later the racemization of amino acids was employed in the determination of the age of any materials containing proteins. Among others it was used to determine the age of deposits: (Bada et al. 1970; Wehmiller and Hare, 1971), shells (Hare and Mitterer, 1968), bones (Bada, 1972; Dungworth et al, 1973), teeth (Helfman and Bada, 1975; 1976) and corals (Wehmiller et al, 1976) as well as for the estimation of the temperatures since their formation (Bada et al, 1973; Schroeder and Bada, 1973). To the best of our knowledge the method of racemization and epimerization of amino acids in the determination of age is not used in Hungary. As the need for the application of this method has been raised repeatedly, the Stock-Breeding Faculty of the Agricultural University at Kaposvár in conjunction with the Museum of the County of Somogy and with the Anthropology Section of the Museum of Natural Sciences has initiated the elaboration of a method which is based on the racemization or epimerization of amino acids. This is an up-to-date method and it can easily be matched with the equipment available in the laboratory

. Our aim has been to elaborate a method applicable for determining the D- and L-amino acid content of fossils, thereby enabling us to judge the age with a reasonable level of accuracy

. 2. Overview of the literature The ratio of the D- and L-amino acids of fossils depends on the method applied in the separation and determination of amino acids. We can obtain varying results in examining free, protein saturated, or total amino acid determinations but the reason for the difference could also be attributed to the differences between the enzyme

, the gas-chromatographic or high pressure liquid chromatographic methods all having a different type of error. The isolation of amino acids from fossils has become possible by the application of several methods, some of which have certain similarities. Generally the samples are