(See facing page.) (A) BLASTP results given theM. tuberculosis Rv1625c protein sequence as query and SwissProtPlus as the database, using the PAM70 matrix. (B) Bayes alignment of the Rv1625c and human CYA8 protein sequences using the PAM matrices. The four residues implicated in catalysis (two aspartates, an aspargine, and an arginine; see text) are in red and the two residues that confer substrate specificity are in blue.