Structure-function modeling of the interactions of N-alkyl-N-hydroxyanilines with rat hepatic aryl sulfotransferase TV

Although previous investigations have clearly shown that N-hydroxy arylamin es and N-hydroxy heterocyclic amines are substrates for sulfotransferases, relatively little is known about which structural features of the N-hydroxy arylamines are important for sulfation to occur. The purpose of this inves tigation was to determine the extent to which secondary N-alkyl-N-hydroxy a rylamines interact with aryl sulfotransferase (AST) IV (also known as tyros ine-ester sulfotransferase or ST1A1) and to evaluate these interactions usi ng molecular modeling techniques. AST IV is a major cytosolic sulfotransfer ase in the rat, and it catalyzes the sulfation of various phenols, benzylic alcohols, arylhydroxamic acids, oximes, and primary N-hydroxy arylamines. In this study, three secondary N-hydroxy arylamines, N-hydroxy-N-methylanil ine, N-ethyl-N-hydroxyaniline, and N-hydroxy-N-n-propylaniline, were found to be substrates for the purified rat hepatic AST IV. However, when the N-a lkyl substituent was an n-butyl group (i.e., N-n-butyl-N-hydroxyaniline), t he interaction with the enzyme changed from that of a substrate to competit ive inhibition. This change in specificity was further explored through the construction and use of a model for AST IV based on mouse estrogen sulfotr ansferase, an enzyme whose crystal structure has been previously determined to high resolution. Molecular modeling techniques were used to dock each o f the above N-hydroxy arylamines into the active site of the homology model of AST IV and determine optimum ligand geometries. The results of these ex periments indicated that steric constraints on the orientation of binding o f secondary N-alkyl-N-hydroxy arylamines at the active site of AST TV play a significant role in determining the nature of the interaction of the enzy me with these compounds.