A new family of small (5 kDa) protein inhibitors of insect alpha-amylases from seeds or sorghum (Sorghum bicolar (L) Moench) have sequence homologies with wheat gamma-purothionins.
Three isoinhibitors of locust and cockroach gut alpha-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 C18. 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 (SI alpha-1) or 48 (SI alpha-2, ST alpha-3) amino acids, and are the smallest plant inhibitors of alpha-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 gamma-purothionins recently isolated from wheat endosperm.
Bloch
C
C
Department of Biological Sciences, University of Durham, UK.
Richardson
M
M
D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides; D002846:Chromatography, Affinity; D007313:Insecta / Q000201:enzymology; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics*; D010944:Plants / Q000201:enzymology*; D012639:Seeds / Q000201:enzymology*; D012689:Sequence Homology, Nucleic Acid; D014118:Toxins, Biological; D014908:Triticum / Q000201:enzymology*; D000516:alpha-Amylases / Q000235:genetics*
D023181:Antimicrobial Cationic Peptides; D010940:Plant Proteins; D014118:Toxins, Biological; C016085:purothionin; D000516:alpha-Amylases