| Ac-Pro-Cys-Lys-Ala-Arg-Ile-DPhe-Pro-Tyr-Gly-Gly-Cys-Arg-NH(,2),(' ).;Ac-Pro-Cys(Acm)-Lys(Z)-Ala-Arg(Tos)-Ile-DPhe-Pro-Tyr(Cl(,2)Bzl)-Gly-Gly-Cys(Acm)-Arg(Tos)-Res was prepared by the Merrifield method. The peptide was removed from the resin as a methyl ester, converted to the amide, and partially deprotected with HF. The Acm-groups were removed and the disulfide bond formed by treatment with I(,2) in AcOH. Purification was by Sephadex G-25 chromatography in 10% AcOH.;In trypsin assays with tosyl arginine methyl ester as substrate, a K(,i) of 2 x 10('-6) M was obtained after a 10 min incubation of inhibitor and enzyme. Using benzoyl arginine p-nitroanilide as substrate, a K(,i) of 1.8 x 10('-6) M was obtained from a Lineweaver-Burk plot. A half-life of inhibition of 15 min was measured. The partially deprotected peptide (with Acm-groups intact) had a K(,i) of 2.6 x 10('-5) M and a half-life of 11 min.;a 13-peptide, has been synthesized and tested for inhibitory activity and stability against trypsin. This peptide contains the sequence -DPHe-Pro- which is known to impose a tight (beta)-turn in Gramacidin S. If a similar turn is formed in the 13-peptide, it will be sequentially and conformationally very similar to the portion of the basic pancreatic trypsin inhibitor (BPTI) which binds to trypsin. |
