Purification and properties of the enzyme arylamine N-acetyltransferase from the housefly Musca domestica

The enzyme arylamine N-acetyltransferase (ANAT) from the housefly (Musca domestica) has been purified. The M(r) of the purified enzyme was 27,600 +/- 1700 as estimated by gel filtration. SDS/PAGE yielded a value of 26,000 +/- 300, clearly indicating a monomeric structure. The purified enzyme had apparent Km values for acetyl-CoA and tyramine of 8.4 microM and 8.8 microM respectively, a pH optimum of 7.2 in 10 mM potassium phosphate buffer and an apparent pI of 5.8. ANAT activity showed a strong dependency on the presence of 2-mercaptoethanol during the purification stages. The enzyme could be completely inactivated by treatment with p-chloromercuribenzoate although the enzyme activity was protected by preincubation with acetyl-CoA. One or more cysteine residues are clearly required for catalytic activity, as demonstrated for the mammalian enzyme. In contrast, partial sequencing of the enzyme has yielded a number of peptide sequences, including the N-terminal sequence, which show no similarity with those reported for the mammalian and avian enzymes.