Elastase-Cathepsin G Inhibitors Eglin b and Eglin c Differ by a Single Tyr ↔ His Substitution. A Micro-Method for the Identification of Amino-Acid Substitution

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Abstract
The structures of eglin B and eglin c, both potent inhibitors of human neutral granulocytic proteinase elastase and catepsin G, were compared by micro amino-acid analysis and peptide mapping techniques. Eglin b and eglin c differ by 1 amino-acid substitution in the middle of the polypeptide chain. Tyr residue at position 35 of eglin c was substituted by His in elgin b. This amino-acid substitution requires 1 base exchange (U .tautm. C) at the DNA level and apparently does not affect the reactive site of eglins. Though without disulfide linkages, eglins are very rigid molecules and can be effectively digested by trypsin only after rigorous acid incubation.