INTERACTION OF 2ND-DOMAIN AND 3RD-DOMAIN OF JAPANESE-QUAIL OVOMUCOID WITH 10 MAMMALIAN TRYPSINS

Second and third domains were prepared from Japanese quail ovomucoid a nd association equilibrium constants, K(a)s, were measured at 25 degre es C and pH 8 for these domains with trypsins from ten mammalian speci es: cat, cow, dog, guinea pig, hog, horse, man, rabbit, rat, and sheep . The values ranged from 10(8) M-1 to 10(10) M-1 for the second domain -trypsin associations and from 10(6) M-1 to 10(8) M-1 for the third do main-trypsin associations. Changes in K-a values for the interactions between the trypsins and each domain are attributed to slight changes in surface conformation caused by the residue changes in the inhibitor -binding region other than the S-1 pocket of the trypsin species. The representative of such residue changes is assumed to be the one observ ed at residue 217 of trypsin molecule. Concerning each trypsin, the K- a value with the second domain was always higher than that with the th ird domain. However, the ratios between the two equilibrium constants varied from 3 to 60 depending upon trypsin species. This means that am ino acid changes in enzyme-contact residues other than the P-1 site of the Kazal-type inhibitor can make it possible to recognize even a sli ght difference in inhibitor-binding surface among the enzymes with the same S-1 pocket and highly similar overall three-dimensional structur e. (C) 1998 Elsevier Science B.V. All rights reserved.