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

Abstract

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.