Human liver arylamine N-sulfotransferase activity. Thermostable phenol sulfotransferase catalyzes the N-sulfation of 2-naphthylamine

Our experiments were performed to determine whether human liver, like that of other mammals, could catalyze the N-sulfation of an arylamine, 2-naphthylamine (2-NA) and, if so, whether this reaction might be catalyzed by one or both of the two known forms of human phenol sulfotransferase (PST). One form of PST is thermostable (TS) and catalyzes the sulfation of ''simple'' phenols such as p-nitro-phenol, while the other form is thermolabile (TL) and catalyzes the sulfate conjugation of phenolic monoamines such as dopamine. When 2-NA that was not contaminated with 2-naphthol was used as substrate, human hepatic cytosol could catalyze the N-sulfation of 2-NA with an apparent K(m) of 322 μM. However, substrate kinetics of the sulfate donor for the reaction, 3'-phosphoadenosine-5'-phosphosulfate, were biphasic, with estimated apparent K(m) values of 0.13 and 2.2 μM for high and low affinity activities, respectively. Human liver arylamine N-sulfotransferase (AANST) activity was similar to that of TS but not TL PST with regard to thermal stability, inhibition by 2,6-dichloro-4-nitrophenol (DCNP), and regulation among individuals. For example, average temperatures that produced 50% inactivation of TL PST, TS PST, and AANST activities, measured with both 0.05 and 1.0 mM 2-NA as substrate, were 35.0, 40.5, 40.3 and 40.5°C, respectively. IC₅₀ values for the inhibition by DCNP of TL PST, TS PST, and AANST, measured with 0.05 and 1.0 mM 2-NA as substrate, were 110, 1.8, 1.3, and 4.0 μM, respectively. In addition, in cytosolic preparations from 20 individual human liver samples, there was a highly significant correlation between TS PST activity and AANST activity measured with both 0.05 mM 2-NA and 1.0 mM 2-NA as substrate (r(s) = 0.899, p < 0.0001 and r(s) = 0.934, p < 0.0001, respectively). However, there was not a significant correlation between TL PST activity and AANST measured with 0.05 mM and 1.0 mM 2-NA as substrate (r(s) = 0.257, p = 0.278 and r(s) = 0.268, p = 0.258, respectively). Finally, partially purified TS PST, but not partially purified TL PST, catalyzed the N-sulfation of 2-NA. However, substrate kinetic studies once again indicated that the partially purified TS PST preparation might contain two AANST activities. In summary, our results were compatible with the conclusion that TS PST was the major enzyme responsible for catalyzing the N-sulfation of 2-NA in human liver cytosol. However, sulfotransferase(s) other than TS PST might also play a role in this reaction.