ABUNDANCE AND STABLE CARBON-ISOTOPE COMPOSITION OF AMINO-ACIDS IN MOLECULAR-WEIGHT FRACTIONS OF FOSSIL AND ARTIFICIALLY AGED MOLLUSK SHELLS

Amino acid abundances in molecular weight fractions (separated by ultr afiltration) of artificially aged carbonate shells and fossil shells a re reported. Hydrolyzable amino acids were primarily concentrated in t he <500 Dalton fraction and in an acid insoluble fraction. With contin ued heating, proteins hydrolyzed to free amino acids and peptides. The amount of amino acids in the acid insoluble fraction diminished where as the amount of amino acids in the <500 Dalton molecular weight fract ion increased. The amount of soluble peptides in molecular weight frac tions between 500 and 10,000 Daltons was minimal in both the heated an d fossil shells. The extent of amino acid racemization was not uniform throughout the molecular weight spectrum. Free amino acids and amino acids in lower molecular weight peptides were racemized to the greates t extent, whereas amino acids recovered from the insoluble residue fra ctions were the least racemized. The deltaC-13 values of individual am ino acids in the molecular weight fractions of the artificially aged s hells generally varied by less-than-or-equal-to 2 - 3 parts per thousa nd relative to their respective values in the total hydrolyzate of the unheated shell. These differences may in part reflect fractionations resulting from hydrolysis and decomposition.