Kinetics of arylamine N-acetyltransferase in tissues from human breast cancer.
N-Acetyltransferase activity and Michaelis-Menten kinetic constants were determined in cancerous and non-cancerous breast tissues from 30 female patients with breast cancer. The results derived from tissue cytosol showed that 12 rapid, ten intermediate and eight slow acetylators based on p-aminobenzoic acid and 2-aminofluorene for substrates. The mean apparent Km values for the monomorphic substrate p-aminobenzoic acid and polymorphic substrate 2-aminofluorene were: 55.0 +/- 18.7, 114.0 +/- 30.0, and 137.0 +/- 37.2 microM; and 62.5 +/- 23.7, 166.0 +/- 67.0, and 239.0 +/- 76.6 microM for the slow, intermediate, and rapid enzymes, respectively. Compared to the enzymes from slow acetylators, the rapid acetylators exhibited mean apparent Vmax values eight- and ten-fold greater for p-aminobenzoic acid and 2-aminofluorene, respectively. A similar trend was obtained from the blood cytosols of cancerous patients and healthy volunteers. N-Acetyltransferase activity of breast cancerous and non-cancerous tissues were 1.5- and 2.2-fold different between rapid and slow acetylator with p-aminobenzoic acid and 2-aminofluorene as substrates, respectively. In breast cancerous tissues, 75% and 70% of the cytosolic N-acetyltransferase activity were inhibited under 2 mM of tamoxifen as substrates of 2-aminofluorene and p-aminobenzoic acid, respectively. Similar results were also found in non-cancerous tissues and blood samples from breast cancer patients and healthy volunteers. The effect of 1 mM tamoxifen on the N-acetyltransferase activity from breast cancerous tissues with positive estrogen receptor was 1.6-fold higher than that of negative estrogen receptor. This is the first demonstration to show that anti-estrogen drug can affect N-acetyltransferase activity in breast cancerous tissues. Therefore, this finding may provide a clue to the use of tamoxifen in prevention of human breast cancer.
Lee
J H
JH
Department of Medicine, China Medical College, Taichung, Taiwan, ROC.
Chung
J G
JG
Lai
J M
JM
Levy
G N
GN
Weber
W W
WW
D010129:4-Aminobenzoic Acid / Q000378:metabolism; D000107:Acetylation; D016588:Anticarcinogenic Agents / Q000494:pharmacology; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism*; D001940:Breast / Q000201:enzymology*; D001943:Breast Neoplasms / Q000201:enzymology*; D002273:Carcinogens / Q000378:metabolism; D005260:Female; D005449:Fluorenes / Q000378:metabolism; D006801:Humans; D009363:Neoplasm Proteins / Q000378:metabolism*; D010641:Phenotype; D013629:Tamoxifen / Q000494:pharmacology
D016588:Anticarcinogenic Agents; D002273:Carcinogens; D005449:Fluorenes; D009363:Neoplasm Proteins; D013629:Tamoxifen; C012177:2-aminofluorene; D001191:Arylamine N-Acetyltransferase; D010129:4-Aminobenzoic Acid