Fossil proteins in vertebrate calcified tissues

Abstract

Selected fossil vertebrates and the enclosing sediments dating from 1300 years B.C. to approximately 400 million years ago were subjected to amino acid assay. The amino acid analyses revealed little evidence of intact collagen in fossils of Tertiary, Mesozoic or Palaeozoic age. There was, however, evidence of contemporary proteinaceous material which may have been derived from bacteria. In Palaeozoic material the analyses detected a general background of amino acids common to both fossils and sediments. The degree of racemization was routinely determined as a means of measuring modern contamination of geologically older samples. An electron microscope study of Quaternary (Pleistocene) collagen revealed a significant reduction of the 64 nm banding to about 50 nm. The same Pleistocene material gave amino acid compositional profiles typical of collagen. However, when this material was subjected to digestion by the proteolytic enzymes collagenase, pronase and subtilisin, the resulting peptide fingerprints showed small but significant differences from those obtained from modern collagen digests, indicating the possibility of changes having occurred during fossilization affecting susceptible cleavage sites in the molecule.