Characterization of the entomocidal parasporal crystal of Bacillus thuringiensis

Abstract

The parasporal crystalline protoxin of B. thuringiensis contains a single glycoprotein subunit that has a MW of .apprx. 1.2 .times. 105. The carbohydrate consists of glucose (3.8%) and mannose (1.8%). At alkaline pH the proendotoxin is apparently solubilized and activated by an autolytic mechanism involving an inherent SH protease that renders the protoxin insecticidal. Activation generates protons, degraded polypeptides, SH group reactivity, proteolytic activity and insect toxicity. Chemical modification of the SH groups inhibits the proteolytic and insecticidal activities, suggesting that cysteine residues may be present in the active site of the protein. [Insecticidal assay was performed with neonate larvae of tobacco hornworm Manduca sexta.].