Eubacterium acidaminophilum is a strict anaerobic, Gram positive, rod-shaped bacterium, which belongs to the cluster XI of the Clostridia. It ferments amino acids in a Stickland type reaction. Glycine can be used as single carbon and energy source. E. acidaminophilum possesses at least eight selenocysteine-containing proteins. One of these, PrpU (probably redoxactive protein with selenocysteine [U]), is a protein with a molecular mass of 11 kDa. So far, PrpU was only identified in E. acidaminophilum and there are no known homologous proteins in any other organism. This protein contains the putative redoxactive motif CxxU and is thought to be involved in the glycine metabolism of E. acidaminophilum. The gene prpU is part of the glycine-decarboxylase operon. It is transcribed polycistronically together with the thf gene and the genes encoding for the glycine-decarboxylase. The transcription of this operon is induced by glycine and seems to be regulated by a glycine-dependent riboswitch. By using a bacterial yeast two-hybrid system and pull-down assays, protein-protein interactions were detected between PrpU and the following proteins: the gcvP2 subunit of the glycine-decarboxylase, the GrdA subunit of the glycine reductase and thioredoxin. The genes encoding for the glycine-decarboxylase were heterologous expressed in E. coli, however, no decarboxylase activity was detected. Therefore, it was not possible to proof an involvement of PrpU in the the glycine metabolic in E. acidaminophilum. The genes for the glycine, sarcosine und betaine reductase und the thioredoxin-system are organized in specific gene clusters.