Molecular basis of the arginase null phenotype of H. pylori clinical isolate A2. A. Arginase activity of H. pylori strain 26695 and clinical isolate A2. B. Variation in the arginase upstream regions of H. pylori strains 26695 and A2. Nine nucleotide differences were noted between these two sequences. C. Variations in the arginase amino acid sequences between H. pylori strains 26695 and A2. Eleven amino acid differences are highlighted (311/322 identity [96% identity]; 316/322 similar [97% similar]. Three amino acid differences (underlined) were found only in strain A2: I174M, S232I, and D257N. D. Arginase activity of E. coli transformed with pQE30-rocF (rocF from strain 26695) and of strains transformed with site-directed mutants of I174M, S232I, and D257N. E. Anti-RocF Western blot analysis of extracts of E. coli transformed with different plasmids including site-directed mutants of RocF. RocF frag indicates degradation product from RocF.