Bálint Laura - Russu Tibor szerk.: A Csíki Székely Múzeum Évkönyve 2005. Természettudományok (Csíkszereda, 2006)

ALKALMAZOTT KÉMIA - ALBERT CSILLA - SALAMON ROZÁLIA - CSAPÓ JÁNOS: FOSSZILIS anyagok korának meghatározása az aminosavak átalakulása és racemizációja alapján

A CSÍKI SZÉKELY MÚZEUM ÉVKÖNYVE 2005 415-438 ALBERT CSILLA - SALAMON ROZÁLIA - CSAPÓ JÁNOS FOSSZILIS ANYAGOK KORÁNAK MEGHATÁROZÁSA AZ AMINOSAVAK ÁTALAKULÁSA ÉS RACEMIZÁCIÓJA ALAPIÁN Abstract: [Determination of fossil materials âge based on the transformation and racemization of amino acids] Racemization of free amino acids is considerably lower than that of amino acids bound in peptide. In the same experimental conditions, the rate of racemization of free amino acids is only 20-80% of that of peptide bound amino acids. When using to tradiţional protein hydrolysis, racemization was 1,2-1,6 times as high as that obtained at high températures (160- 180 °C), under conditions ensuring total hydrolysis of the protein. This lower degree of racemization may be explained by the fact that, at high températures, the protein hydrolyses more rapidly into free amino acids and the racemization of free amino acids is considerably slower that of amino acids bound in Polypeptides. When hydrolysis is conducted at lower températures for longer times, the amino acids bound in the peptide chain are exposed for a longer time to the effects actually causing racemization. As a resuit, we may say that any factor which speeds up hydrolysis, will lower the degree of racemization. High température hydrolysis (at 160 °C for 45 to 60 minutes, at 170 °C for 30 - 45 minutes and 180 °C for 30 minutes) are recommended for those who would like to hydrolyse the protein for short times and to determine the degree of racemization occurring in the Polypeptide chain, but do not wish to use enzyme hydrolysis. After developing protein hydrolysis method with low racemization, a method has been developcd to determine the âge of fossil bone samples based on amino acid racemization (AAR). Approximately one hundred fossil bone samples of known âge from Hungary were collected and analysed for D- and L-amino acids. As the racemization of amino acids is affected by température, pH, metal content of the soil, and time passed since death, thèse factors were eliminated by comparing the estimated âge to âge determined by the radiocarbon method. Determining the D- and L- amino acid contents in samples of known âge, determining the half life of racemization and plotting the D/L ratio as a function of time, calibration curvcs were obtained. These curves can be used for the âge estimation of samples after determining their Dand L- amino acid content. The D/L ratio for 2 to 3 amino acids was determined for each sample and the mean value of estimated âges based on calibration curves was considered to estimate âge of the fossil samples. After this a method for évaluation of âge of wool carpets and textiles was developed based on the âge dependent altération of amino acid composition of proteins. Samples of 23 wool carpets and textiles of known âge, obtained from the Hungárián Museum of Industrial Arts and the Hungárián National Museum were analysed for amino acid content. Results were compared with data obtained for contemporary, untreated wool and wool carpet. The cysteic acid content of wool increased with age. The contemporary wool carpet contained 0,31 g of cysteic acid in 100 g of protein. Comparable figures were 1,87 g for 550-year old carpet and 4,01 - 4,39 g for the 1600 - 1750-year old wool carpets. Cystine content decreased with age corresponding figures being 7,88, 3,12, 1,19-0,97, respectively. Corresponding contents of methionine were 0,43, 0,21, and 0,20-0 and for tyrosine were 3,07, 2,11 and 0,20 - 0. Prédiction équations were developed as linear régressions of age of wool on cysteic acid, cystine and tyrosine con-