Anhydrotrypsin: new features in ligand interactions revealed by affinity chromatography and thionine replacement

Anhydrotrypsin was isolated in high purity from the product of base elimination from phenylmethanesulfonyl-trypsin, by a single operation of affinity chromatography. The adsorbent used for the chromatography was an agarose derivative coupled with peptides containing C-terminal arginine residues. As the affinity of the adsorbent for anhydrotrypsin was high compared with that for trypsin, purification of the enzyme derivative was easily achieved without the prior inactivation of trypsin which had been regenerated during the elimination reaction. Comparative studies of the ligand interaction specificities with anhydrotrypsin and trypsin confirmed the stronger interaction of the former protein with product-type ligands such as Bz-Arg-OH. No marked differences were observed between them in affinities toward substrate-type ligands such as Bz-Arg-NH2. The higher affinity of anhydrotrypsin was found to be limited to product-type ligands of L-configuration, i.e., the protein displayed an ability to discriminate the L-ligand from its optical isomer. THE PKa value for the ionization form of anhydrotrypsin responsible for the interaction with Bz-Arg-OH was estimated to be 7.60+/-0907