PURIFICATION AND PROPERTIES OF THE ENZYME ARYLAMINE N-ACETYLTRANSFERASE FROM THE HOUSEFLY MUSCA-DOMESTICA

The enzyme arylamine N-acetyltransferase from the housefly (Musca domestica) has been purified. The M(r) of the purified enzyme was 27600+/-1700 as estimated by gel filtration. SDS/PAGE yielded a value of 26000+/-300, clearly indicating a monomeric structure. The purified enzyme had apparent K(m) values for acetyl-CoA and tyramine of 8.4 muM and 8.8 muM respectively, a pH optimum of 7.2 in 10 mM potassium phosphate buffer and an apparent pl 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 hy 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.