State of preservation of polymorphic plasma proteins recovered from ancient human bones

Protected by the mineral matrix, bone proteins are capable of surviving inh umation periods of several hundreds or thousands of years in soil. While th e preservation of the bone matrix protein, collagen I, is the prerequisite for a variety of archaeometric approaches, such as radiocarbon dating and t he 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 s pecific demands of these aged proteins, since they are not only degraded an d fragmented but also cross-linked to other organic components, either indi genous to the bone or to contaminants from the burial environment. Complete decomposition phenomena are responsible for the altered mode of migration of aged proteins through a gel. After isoelectric focusing, the ancient pro teins mainly concentrate below pH 4.45 in the pH gradient. Thus, highly neg atively charged protein components have a better chance of preservation in bone after death. Isoelectric focusing with subsequent immunoblotting of an cient 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., x2-HS-glycoprotein and x1-antitrypsin). Never theless, in combination with different immunological analyses, previous res ults concerning the selective enrichment of x2-HS-glycoprotein in bone comp ared with other plasma glycoproteins could be confirmed.