University of Innsbruck Austria 1 article published in JoVE Biochemistry Expression, Purification, Crystallization, and Enzyme Assays of Fumarylacetoacetate Hydrolase Domain-Containing Proteins Alexander K. H. Weiss1,2, Max Holzknecht1,2, Elia Cappuccio1,2, Ilaria Dorigatti1, Karin Kreidl1, Andreas Naschberger3, Bernhard Rupp3, Hubert Gstach4, Pidder Jansen-Dürr1,2 1Research Institute for Biomedical Aging Research, University of Innsbruck Austria, 2Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck Austria, 3Division of Genetic Epidemiology, Medical University of Innsbruck Austria, 4Faculty of Chemistry, Department of Organic Chemistry, University of Vienna Austria Expression and purification of fumarylacetoacetate hydrolase domain-containing proteins is described with examples (expression in E. coli, FPLC). Purified proteins are used for crystallization and antibody production and employed for enzyme assays. Selected photometric assays are presented to display the multi-functionality of FAHD1 as oxaloacetate decarboxylase and acylpyruvate hydrolase.