Fig. 24.

Schematic of intra-crystalline amino acids entrapped within carbonate crystals. Unlike the proteins of the organic matrix between the crystallites, which leach from the shell with time, amino acids are entrapped in the closed intra-crystalline system. Thus the relation between the D/L values of different amino acids and between free (non-protein bound) and total hydrolysable (both free and originally protein-bound amino acids, released by acid hydrolysis) amino acids is predictable. Analysis of the whole shell results in lower-than-expected D/L values for the THAA, due to the loss of the more highly racemized FAA.