| Abstract: |
Protected by the mineral matrix, bone proteins are capable of surviving inhumation periods of several hundreds or thousands of years in soil. While the preservation of the bone matrix protein, collagen I, is the prerequisite for a variety of archaeometric approaches, such as radiocarbon dating and the reconstruction of palaeodiet by stable isotope analysis, little is known about both the rate and state of preservation of non-collagenous proteins. We succeeded in the isolation, electrophoretic separation (SDS-PAGE, IEF) and immunological detection (radial immunodiffusion, IEF immunoblotting and ELISA) of plasma proteins preserved in archaeological human bones. However, sample preparation and electrophoretic methods had to be adapted to the specific demands of these aged proteins, since they are not only degraded and fragmented but also cross-linked to other organic components, either indigenous to the bone or to contaminants from the burial environment. Complex decomposition phenomena are responsible for the altered mode of migration of aged proteins through a gel. After isoelectric focusing, the ancient proteins mainly concentrate below pH 4.45 in the pH-gradient. Thus, highly negatively charged protein components have a better chance of preservation in bone after death. Isoelectric focusing with subsequent immunoblotting of ancient protein samples revealed protein patterns which showed marked charge-modifications in comparison with those of modern human plasma proteins due to protein degradation (e.g. a2-HS-glycoprotein and a1-antitrypsin). Nevertheless, in combination with different immunological analyses, previous results concerning the selective enrichment of a2-HS-glycoprotein in bone compared with other plasma glycoproteins could be confirmed.
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