Structure and function of a microbial allantoin racemase reveal the origin and conservation of a catalytic mechanism Laura Cendron 1,4,a , Ileana Ramazzina 2,5,a , Vincenzo Puggioni 2 , Eleonora Maccacaro 2 , Anastasia Liuzzi 2 , Andrea Secchi 3 , Giuseppe Zanotti 1 , Riccardo Percudani 2* . 1 Department of Biomedical Sciences, University of Padova, Padova, Italy. 2 Department of Life Sciences, University of Parma, Parma, Italy. 3 Department of Chemistry, University of Parma, Parma, Italy. 4 Present address: Department of Biology, University of Padova, Padova, Italy. 5 Present address: Department of Biomedicine, Biotechnology and Translational Research, University of Parma, Parma, Italy. a Equal contribution authors Supplementary information Table S1. Genome accessions of the Pseudomonas species previously tested for AllR activity. Table S2. Primers for PfAllR ampliication and mutagenesis. Figure S1. 13 C NMR data for the enzyme-catalyzed and uncatalyzed C2-C7 isotopic exchange of allantoin. Figure S2. 1 H NMR data for the enzyme-catalyzed and uncatalyzed proton-deuterium exchange of allantoin. Figure S3. Organism distribution of the diferent groups of the Asp/Glu racemase superfamily.