Inactivation of Scytalidium lignicolum acid protease B with 1,2-epoxy-3-(4'-azido-2'-nitrophenoxy)propane.

Abstract

The acid protease B of Scytalidium lignicolum (SAB) was modified with l, 2-epoxy-3-(4'-azido2'-nitrophenoxy)propane [EANP] under acidic conditions. EANP was incorporated stoichiometrically into SAB, and the enzyme was almost completely inactivated. The modified enzyme was digested with thermolysin and EANP-labeled peptides were separated by high performance liquid chromatography (HPLC). The amino acid sequence of the major peptide labeled was Ile-Leu-Glu-Thr-Gly, which corresponds to the sequence of residue Nos. 51-55 of the enzyme. Treatment of the peptide with 0.5 N hydroxylamine (pH 10.5) resulted in the complete removal of the modifier from the labeled peptide, suggesting that EANP is ester-linked to the Glu-53 residue of the enzyme. The amino acid sequence (-Cys-Gln-Thr-Ala-Ile-Leu-Glu-Thr-Gly-) around Glu-53 of SAB shows high homology with those around the active site aspartic acids of calf chymosin and porcine pepsin. The results indicate the involvement of Glu-53 in the enzyme reaction of SAB.