PURIFICATION AND CHARACTERIZATION OF THE UREASE ENZYMES OF HELICOBACTER SPECIES FROM HUMANS AND ANIMALS

The urease enzymes of Helicobacter pylori, H. mustelae, H. felis, and H. nemestrinae have been purified to homogeneity by affinity chromatography and characterized. The native urease enzymes of the four organisms were found to be almost identical, with a pI of 6.1 and molecular masses of 480 to 500 kDa, as determined by electrophoretic mobility in nondenaturing polyacrylamide gels. Transmission electron microscopy of the native urease showed it to be a molecule approximately 13 nm in diameter, with hexagonal symmetry. Denaturation studies indicated that each urease enzyme molecule was composed of two nonidentical subunits with molecular masses of approximately 64 and 30 kDa. The subunits were present in a 1:1 ratio, suggesting a hexameric stoichiometry for the native molecule. The predicted molecular mass of H. pylori urease, based on subunit molecular weight and stoichiometry, is 568 kDa. N-terminal amino acid sequencing of the enzyme subunits from the four species revealed high levels of homology. The large subunits (UreB) were found to be 92 to 100% homologous, and the small subunits (UreA) were 75 to 95% homologous over the first 12 to 20 residues. The high degree of homology suggests a common ancestral origin and an important role for the urease enzymes of these organisms.