A STEREOCHEMICAL PROBE OF THE TETRAHEDRAL INTERMEDIATE IN THE REACTIONS OF ACETYL-COENZYME-A DEPENDENT ACETYLTRANSFERASES

A pair of isomeric acetyl-coenzyme A (acetyl-CoA) analogs have been pr epared in which the thioester group is replaced with a secondary alcoh ol. The two isomers differ in stereoconfiguration of the secondary alc ohol and were designed to mimic the two possible configurations of the tetrahedral intermediate or transition state in the reactions of acet yl-CoA dependent acetyltransferases. These two isomers were tested as inhibitors of chloramphenicol acetyltransferase and carnitine acetyltr ansferase, both of which have previously been predicted to form a tetr ahedral intermediate which matches the configuration of the (S)-alcoho l. The (S)-isomer was the more potent inhibitor of both enzymes, with K-i values 12-fold and 6-fold lower than the K-i values for the (R)-is omer, The (S)-isomer was also the more potent inhibitor of phosphate a cetyltransferase, acetyl-CoA synthetase, and arylamine acetyltransfera se, for which the stereochemistry of the tetrahedral intermediate was previously unknown. These results suggest a common stereoconfiguration of the tetrahedral intermediate among acetyl-CoA dependent acetyltran sferases.