Sheep tissue acetyl coenzyme A-dependent arylamine N-acetyltransferases

Acetyl coenzyme A-dependent arylamine N-acetyltransferases (NATs), EC 2.3.1.5. were measured in sheep tissues (N = 14) using p-aminobenzoic acid (PABA) as a substrate. Specific activities of liver, kidney, and lung NATs were 5.3 x 10(-3) +/- 1.4 (mean +/- SE) nmoles.min-1.mg protein-1, 3.4 x 10(-3) +/- 1.1 nmoles.min-1.mg protein-1, 2.5 x 10(-3) +/- 1.2 nmoles.min-1.mg protein-1, respectively. Km values were 53 +/- 3 microM for liver, 34 +/- 2 microM for kidney, and 28 +/- 2 microM for lung tissue. Optimum pH for the acetylation reaction was found as 7.5. The enzyme activity was stable for at least 6 months in all tissues, when stored at -70 degrees C. The enzyme from sheep tissues were quite heat-stable. Inhibition studies showed that N-ethylmaleimide was a potent inhibitor of sheep tissue NAT enzymes.