Slow rates of degradation of osteocalcin: Green light for fossil bone protein?

Our claim, published in this journal, for successful immunodetection of the protein osteocalcin in dinosaur bone has been challenged on the grounds th at the findings are inconsistent with the kinetics of decomposition. Here w e show that the close association of osteocalcin to the bone mineral vastly enhances its preservation potential relative to the same protein in aqueou s solution. We conducted heating experiments (75-95 degreesC) of modern bon e powder and monitored the survival of three different regions of osteocalc in (N-terminal, His(4)-Hyp(9); C-terminal, Phe(45)-Val(49); and the mid-reg ion, Pro(15)-Glu(31)) with monoclonal antibodies. Extrapolation of our data to 10 degreesC ambient burial temperatures indicates that preservation of the gamma -carboxylated midregion in fossil bone cannot be excluded on kine tic grounds. Clearly, in situ sequence analysis will be the only method by which the preservation of fossil macromolecules will be unequivocally estab lished. Nevertheless, our findings demonstrate the importance of mineral as sociation to protein survival, as was borne out by an investigation of Holo cene (ca. 6 ka) bones. Only in those samples with little recrystallization was the gamma -carboxylated mid-region well preserved. These results imply that the future success of ancient biomolecule research largely depends on our understanding the interaction between these materials and their environ ment throughout diagenesis.