Sulfation of aromatic hydroxamic acids and hydroxylamines by multiple forms of human liver sulfotransferases.

Abstract

Sulfation activity towards various heterocyclic and homocyclic aromatic hydroxamic acids and hydroxylamines was determined in adult human liver cytosol and with partially purified human liver sulfotransferases (STs). In adult human liver cytosols comparable ST activities towards N-hydroxy-2-acetyl-amino-5-phenylpyridine (N-OH-2AAPP), N-hydroxy-4-acetylaminobiphenyl (N-OH-4AABP) and N-hydroxy-4'fluoro-4-acetylaminobiphenyl (N-OH-4FAABP) were found, while the sulfation rates towards N-hydroxy-2-acetylaminofluorene (N-OH-2AAF), N-hydroxy-2-acetylaminonaphthalene (N-OH-2AAN), N-hydroxy-2-acetylaminophenanthrene (N-OH-2AAP) and N-hydroxy-4-acetylaminostilbene (N-OH-4AAS) were two- to five-fold lower. In adult liver cytosol ST activity was found towards all hydroxylamines tested. No significant differences were found for the various hydroxylamines. In general, the ST activities towards the various hydroxamic acids and hydroxylamines were comparable to phenol ST activity using adult liver cytosols. Partial purification of adult human liver STs was achieved by DEAE-Sepharose chromatography followed by anion exchange FPLC. Two separated protein peaks showing both N-OH-2AAPP and N-OH-2APP ST activities were observed and were designated human hydroxylamine/hydroxamic acid sulfotransferase (hHST) 1 and 2. Immunoblot analysis using an anti-rat estrogen ST antibody demonstrated cross reactivity with both hHSTs at a subunit mol. wt of 32 kDa corresponding to the phenol-sulfating form of phenol ST (P-PST). ST activity towards dopamine was low with both hHSTs, but hHST1 also contained significant capacity to sulfate dehydroepiandrosterone. The highest ST activity towards N-OH-2AAPP and N-OH-2APP was measured at pH 5.5 with both hHSTs. The Km values of the two hHSTs for sulfation of N-OH-2AAPP and N-OH-2APP were comparable, while the Vmax values for sulfation of N-OH-2APP were higher than for N-OH-2AAP with both hHSTs. FPLC anion exchange analysis of human platelet STs demonstrated that sulfation of N-OH-4ABP and N-OH-4AABP was associated with P-PST rather than M-PST (platelets do not possess any significant DHEA ST activity). Our results show that the various hydroxamic acids and hydroxylamines are converted by at least two hHSTs. The results presented here for the human liver hydroxamic acid and hydroxylamine ST activities are discussed in relation to those observed in the rat.