... serineproteases do not have an aspartate as the catalytic apparatus.However, for chymotrypsin-type serine proteases, thereplacement of this aspartate with an alanine diminishesprotease activity 104-fold ... 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, ... & Petsko, G .A. (1986) Amino–aromatic interactions in proteins. FEBS Lett. 203, 139–143.19. Chakrabarti, P. & Samanta, U. (1995) CH/, p interaction in thepacking of the adenine ring in...