An iron-sulfur flavoenzyme. The enzyme was originally discovered in the uracil-fermenting bacterium, Clostridium uracilicum, which utilizes uracil and thymine as nitrogen and carbon sources for growth [1]. Since then the enzyme was found in additional organisms including Alcaligenes eutrophus [2], Pseudomonas strains [3,4] and Escherichia coli [5,6].