NAT2 and colorectal carcinoma: To determine the kinetic parameters underlying acetylation of the NAT2_5, NAT2_7 and NAT2_14 protein variants, cells were treated with increasing concentrations of the cytotoxic NAT2 substrate APA, a substrate for which a 40-fold increased affinity was observed in rapid NAT2_4 versus slow NAT2_6 CRC cells11.