A new family of small (5 kDa) protein inhibitors of insect α‐amylases from seeds or sorghum (Sorghum bicolor (L) Moench) have sequence homologies with wheat γ‐purothionins

摘要

>Three isoinhibitors of locust and cockroach gut α-amylases were purified from seeds of sorghum by saline extraction, precipitation with ammonium sulphate, affinity chromatography on Red-Sepharose and preparative RP-HPLC on Vydac C???. The complete primary structures were determined by automatic degradation of the intact reduced and S-alkylated proteins, and by manual DABITC/PITC microsequencing of peptides obtained from enzyme digests. The inhibitors consist of 47 (Slα-1) or 48 (Slα-2, STα-3) amino acids, and are the smallest plant inhibitors of α-amylase currently known. The sequences of the three isoinhibitors exhibit between 38% and 87% identity among themselves and also have homology (32–81%) with the γ-purothionins recently isolated from wheat endosperm.