| Abstract
| - Although previous investigations have clearly shown that N-hydroxy arylamines andN-hydroxy heterocyclic amines are substrates for sulfotransferases, relatively little is knownabout which structural features of the N-hydroxy arylamines are important for sulfation tooccur. The purpose of this investigation was to determine the extent to which secondary N-alkyl-N-hydroxy arylamines interact with aryl sulfotransferase (AST) IV (also known as tyrosine-ester sulfotransferase or ST1A1) and to evaluate these interactions using molecular modelingtechniques. AST IV is a major cytosolic sulfotransferase in the rat, and it catalyzes the sulfationof various phenols, benzylic alcohols, arylhydroxamic acids, oximes, and primary N-hydroxyarylamines. In this study, three secondary N-hydroxy arylamines, N-hydroxy-N-methylaniline,N-ethyl-N-hydroxyaniline, and N-hydroxy-N-n-propylaniline, were found to be substrates forthe purified rat hepatic AST IV. However, when the N-alkyl substituent was an n-butyl group(i.e., N-n-butyl-N-hydroxyaniline), the interaction with the enzyme changed from that of asubstrate to competitive inhibition. This change in specificity was further explored throughthe construction and use of a model for AST IV based on mouse estrogen sulfotransferase, anenzyme whose crystal structure has been previously determined to high resolution. Molecularmodeling techniques were used to dock each of the above N-hydroxy arylamines into the activesite of the homology model of AST IV and determine optimum ligand geometries. The resultsof these experiments indicated that steric constraints on the orientation of binding of secondaryN-alkyl-N-hydroxy arylamines at the active site of AST IV play a significant role in determiningthe nature of the interaction of the enzyme with these compounds.
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