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
Hare (1971) as follows: at the breaking of the protein chain amino acids in activated state show a better tendency for racemization than the bound ones. Bada and Schroder (1972) believe that it is much more probable that the racemization of free amino acids originating from proteins is catalysed by the traces of heavy metal ions, therefore the racemization of amino acids of fossils is a very complicated and complex process, which is effected by hydrolysis and by catalytic effectes (Bada, 1975). It follows that free amino acids, peptides and proteins go through a different racemizational process, and from the three fractions proteins are the most stable from this point of view, as they are not very sensitive to the catalysis of metals. The racemization of free amino acids is mainly effected by the pH (Bada, 1972) and by the metal ions (Ca 2+ , Mg 2+ ). Smith et al. (1976) have proven that ion strength is a major factor as well, and with its increase racemization increases too. By evaluating the aforementioned it can be concluded that racemization differs for free, for peptide tied, and for protein amino acids, and that for these three fractions racemization is also affected to varying degrees by environmental conditions. It seems that protein bound amino acids are the least sensitive to pH and ions therefore this is the most reliable of the three as a tool in determining ages. However, the fact that under alkaline conditions racemizational processes are speeded up,indicates that alkali extraction should preferably be avoided from protein extraction processes. In spite of this, free amino acids and peptide fractions can also provide valuable information for archeologists. 4. Materials and methods 4.1. Sample preparation The sample arriving at the laboratory tobe analysed is free of mechanical contaminations and then washed in running water. It is then dried in a vacuum chamber at room temperature for one night, following which it is ground in a porcelain cup to the finesses of flour. The non-polar contaminations are separated in a Soxhlet appliance for six hours, and after the fumes have been removed a repeated homogenization takes place. The ground sample is suspended in 0.1 mole hydrochloric acid, and the amino acids resulting from the decomposition of protein are separated from the sample for a period of one night (approx. 16 hours). Then the sample is filtered in a G-4 filter, the fre.. amino acid fraction is stored in a refrigerator, and the filtered remainders containing the protein are dneu and homogenized once again. The raw protein content of the resulting material is determined in a Kjei Foss 16-200 type nitrogen analyser, and as a function of the content 100-1000 mg of the material (which is approximately equivalent to 10-20 mg of protein) is hydrolysed with 6 mole hydrochloric acid at 110 °C for a period of 24 hours. Following the completion of the hydrolysis the hydrocliloric acid is removed from the sample bylyophilization, and the silicates separated during the water solution are separated by centrifuging from the liquid containing the free amino acid. The pH of the solution is adjusted with sodiumhydroxide at pH =9, and tire separated calcium, magnesium and heavy metal hydroxides are separated by filtering or by repeated centrifuging from the free amino acids. Following the removal of the hydroxides the pH is immediately adjusted between 6 and 7, and the obtained solution is dried by lyophilization. The resulting material is now ready for the determination of D- and L-amino acids,isoleucine and D-alloisoleucine. r different phases of age determination based on the racemization of amino acids ar < trated in the Appendix.
