... Yokota3 and Fumio Sakiyama2,*1School of Materials Science, Japan Advanced Institute of Science and Technology, Ishikawa, Japan;2Institute for Protein Research,Osaka University, Suita, Osaka, ... Osaka, Japan;3School of Knowledge Science, Japan Advanced Institute of Science and Technology,Ishikawa, JapanAchromobacter protease I (API) has a unique region of aromatic ring stacking with ... suggesting thatAPI has a catalytic quadruple apparatus, composed of Ser194, His57, Asp113 and His210, rather than a catalytictriad.ACKNOWLEDGEMENTWe are grateful to Dr. T. Yamazaki for NMR measurements,...