Effects of four chemicals on N-acetyltransferase activities in human U937 cell line

The effects of p-aminobenzoic acid (PABA), procainamide (PA), anisidine (AN) and isoniazid (INH) on N-acetyltransferase (NAT) activities in cultured human cells were determined. PABA increased the specific activity of PABA NAT in the U937 cells but not in the Hep G2 cells. The enzyme activity in the PABA-treated U937 cells was restored to normal within 4 d after removing PABA from medium. These results imply that the PABA NAT activity in the U937 cells can be induced by PABA and the PABA NAT in the U937 cells is different from that in the Hep G2 cells. INH increased the INH NAT specific activity in the U937 cells but decreased the PABA NAT activity. AN decreased both the AN NAT and the PABA NAT specific activities in the U937 cells. PA did not affect the specific activities of PABA NAT or glucose-6-phosphate dihydrogenase (G-6-P DH) in the U937 cells. PABA also increased the specific activities of AN NAT and G-6-P DH. This implies that the induction effect of PABA on the PABA NAT activity is not specific. In this study the PABA NAT specific activity was increased only by PABA, and the INH NAT activity only by INH. However, the AN NAT activity could be induced by PABA but not by AN. These results indicate that induction of some but not all NAT activities has a limiting specificity.