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.