Abstract: This invention is directed to N.sup..alpha. -acetyltransferase with a molecular weight of about 180,000 daltons, said N.sup..alpha. -acetyltransferase being composed of two subunit peptides having molecular weights of about 95,000 each, having enzyme activity greater than 100 wherein one unit of activity is defined as 1 pmol of acetyl residues incorporated into adrenocorticotropic hormone (ACTH) (amino acids 1-24) under standard assay conditions. This invention is further directed to a method for purifying the N.sup..alpha. -acetyltransferase.