Kinetics of acetyl CoA: Arylamine n‐acetyltransferase from human hepatocellular carcinoma

Abstract

N‐acetyltransferase (NAT) activity and Michaelis‐Menten kinetic constants were determined in hepatocellular carcinoma and non‐cancerous liver tissues from thirty patients. The results derived from tissues showed that 5 rapid, 9 intermediate and 16 slow acetylators based on 2‐amino‐fluorene and p‐aminobenzoic acid as substrates. Overall, the normal liver NAT activity was higher than the cancerous liver NAT activity. The activities (mean ± SD) of NAT from normal and cancerous liver was 3.60 ± 0.98 and 2.18 ± 0.44 nmol/min/mg protein for the acetylation of aminofluorene, and 3.02 ±0.69 and 1.98 ±0.42 nmol/min/mg protein for the acetylation of p‐aminobenzoic acid. Compared to the enzymes from slow acetylators, the rapid acetylators exhibited mean apparent K m and V max values 2.4‐ and 2.6‐, 2.4‐ and 2.7‐fold greater for 2‐amino‐fluorene and /7‐aminobenzoic acid, respectively. In the hepatocellular carcinoma and normal liver tissues, 65% and 58%, 33% and 36% of NAT activities were inhibited under 2.0 mM of 5‐fluorouracil and tamoxifen as substrate of 2‐aminofluorene. But the interferon‐alpha did not show any inhibition of NAT activity in both examined tissues. This is the first demonstration to show that 5‐fluorouracil and tamoxifen can affect NAT activity in human hepatocellular carcinoma. Therefore, this finding may provide a clue to use 5‐fluorouracil and tamoxifen in prevention of human hepatocellular carcinoma.