Crystal-forming proteins of Bacillus thuringiensis. The limited hydrolysis by endogeneous proteinases as a cause of their apparent multiplicity.

The crystals of the entomocidal protein of Bacillus thuringiensis are admixed with proteinases that in the course of their dissolution cause gradual degradation of the "genuine" crystal-forming protein components (i.e. the primary biosynthetic products) to products of lower molecular weight. This phenomenon might explain at least partially the contradictory data on the molecular parameters of the crystal-forming proteins. Preliminary inactivation of the proteinases adsorbed on the crystals allowed us to eliminate this source of the artefacts and to gain more reliable data on the protein composition of the crystals formed by various strains of B. thuringiensis. It has been shown that the crystals formed by all serotypes of B. thuringiensis, with the exception of the serotype V, contain only one protein with a mol. wt. of 145000, 135000 or 130000, depending on the strain. The majority of the strains that belong to the serotype V form crystals consisting of two proteins with mol. wts. of 135000 and 130000, but some of them also have a third component with a mol. wt. of 65000.