Purification of APCE. Coomassie blue–stained gel analysis of the activity pool from each purification step. Proteins were analyzed on a 10% to 20% gradient SDS-PAGE under reducing conditions. STD indicates molecular-weight standards; A, ammonium sulfate fraction (15%-40%); P, phenyl-Toyopearl chromatography fraction; Q, Q-Sepharose chromatography fraction; T, T-gel thiophilic chromatography fraction; and I, immunoaffinity chromatography fraction.