Title: Utilization of Proteomic Techniques for the Identification of Potential Contaminantrelated Biomarker - Environmental Proteomics Authors: Heike Helmholz1, Željka Strižak2, Christiane Ruhnau1, Marijana Erk2, Andreas Prange1 1 Helmholtz-Zentrum Geesthacht, Institute for Coastal Research; Marine Bioanalytical Chemistry, Geesthacht, Germany 2 Ruđer Bošković Institute, Division for Marine and Environmental Research, Zagreb, Croatia Abstract: Contaminants are continually entering the aquatic environment and can cause harmful effects in resident biota such as mussels, which are used worldwide as sentinel bioindicator for chemical stress. In order to detect specific responses on the molecular level and to identify prognostic protein biomarker related to the impact of hazardous substances the methodologies and techniques of proteome investigation provide prolific opportunities for environmental research. In particular variations in protein expression could indicate the exposure to and effect of contaminants. In contrast to frequently used assay systems, which allow the detection of selected markers at the protein level, proteomic techniques enable the detection of changes of protein expression profiles, which allow a much better insight into the multitude of contaminant related effects, simultaneously. In consequence a set of proteins can be identified as indicators for environmental stress. This contribution describes methodological developments to analyze various types of tissue preparations of Mytilus sp. transplanted to differently exposed sites in the North Sea and the Adriatic Sea. Hereby the response against inorganic contaminants is of special interest. Proteins obtained from tissue preparations of gills and digestive glands have been analysed by two dimensional gel electrophoresis (2D GE) and evaluated by gel imaging and 2D GE software (Delta 2D). Differentialy expressed spots have been selected and analyzed by matrix assisted laser desorption/ionisation – time of flight – mass spectrometry (MALDI-ToF-MS). Hints for proteins involved in the metabolism of the amino acid cystein, especially enriched in metallothioneins as indicators for metal exposure, have been found. Furthermore an altered expression of cytoskeletal proteins could be detected. Currently the identification of further potential biomarker of physiologically well defined mussel groups is in progress.