A REACTIVE ASPARTYL RESIDUE OF PEPSIN

Recently it was reported (Hamilton, Spona, and Crowell, 1967) that pepsin was inactivated by an equimolar amount of 1-diazo-4-phenylbutanone-2 (DPB). The results indicated that the reaction occurred at or near the active site of pepsin. In the present communication we report evidence indicating that DPB reacts with pepsin to form an ester of 1-hydroxy-4-phenylbutanone-2 (HPB) with the β-carboxyl group of an aspartyl residue, and that the amino acid sequence containing this aspartyl residue is: Ile-Val-Asp-Thr. This aspartyl residue is different from that attacked by another class of pepsin inhibitors, the α-haloketones (Erlanger, Vratsanos, Wassermann, and Cooper, 1966). Therefore, the present results define a different section of the pepsin molecule which may be involved in the enzymic catalysis. © 1968.