Structure of Helicobacter pylori urease. A: The urease enzyme subunit UreAB (UreA, blue; UreB, cyan; PDB code: 1E9Z); B: The active sites of H. pylori urease with the side chains of the enzyme involved in the chelation of the catalytic di-nickel center shown (Ni, green; O, red; N, blue; C, pink). H. pylori: Helicobacter pylori.