IDENTIFICATION AND CHARACTERIZATION OF 2 ISOZYMIC FORMS OF ARYLAMINE N-ACETYLTRANSFERASE IN SYRIAN-HAMSTER SKIN

Arylamine N-acetyltransferase (EC 2.3.1.5) activity was examined using skin from Syrian hamster. Two isozymes of arylamine N-acetyltransfera se, designated NAT-1 and NAT-2, were detected on anion-exchange high-p erformance liquid chromatography analysis. Both enzyme activities had indistinguishable molecular masses (30 kDa), but differed significantl y in their specificity toward the aromatic amines including serotonin, dopamine, methoxytryptamine, tryptamine, para-phenetidine, para-amino benzoic acid, and sulphamethazine. Specifically, NAT-2 but not NAT-1 c atalyzed acetylation of dopamine to N-acetyldopamine and acetylation o f serotonin to form N-acetylserotonin, a direct precursor of melatonin . The two isozymes were also distinguishable based upon their sensitiv ity toward methotrexate inhibition (50% inhibiting dose for NAT-1 = 38 0 muM; NAT-2 > 2 mM). The presence of these two activities in the skin raises new questions about the physiologic role of this enzyme in gen eral and in the skin-specific functions in particular.