A new class of Bacillus thuringiensis delta-endotoxins, or insecticidal control proteins (ICPs), is defined by an apparently cryptic protein with a unique primary structure and novel entomocidal specificity for certain coleopteran and lepidopteran species. The discovery of a new group of ICPs will extend the use of this natural insecticide in integrated pest-management systems.

Streptomyces peucetius ATCC 29050, a producer of anthracycline antineoplastic agents, was investigated for the expression of intracellular and extracellular azocaseinase activities as a function of growth and medium conditions. When cultures were grown in either nitrate-containing defined medium or glucose-yeast extract complex medium, the intracellular proteolytic activity was greatest during early to mid stationary phase, whereas the extracellular proteolytic activity was produced in late stationary phase. All of the proteolytic activity detected against azocasein was of a serine-type protease activity. These late-occurring proteases may have some function in cellular turnover associated with secondary metabolism and (or) morphogenesis.

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The major serine proteinase of Streptomyces sp. strain C5-A13, a proteinase-overproducing mutant strain, was purified to homogeneity. It has a relative molecular mass (Mr) of 19500 as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Superose-6 gel filtration chromatography, a low isoelectric point, optimal activity at pH 8.5-9.5, and an optimal temperature of approx. 55 ° C. This purified enzyme has a high specific activity on azocasein of 11000 units'rag -1 of protein, a Km of 2.7 X 10 -5 M and a Vmax of 2.0 gmol. rain -1. m g -1 of protein when succinyl-alanyl-alanyl-prolyl-phenylalanine p-nitroanilide was used as substrate. It was inhibited by the serine proteinase inhibitors diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride but not by ethylenediaminetetraacetate (EDTA) or N-tosyl-L-phenylalanine chloromethyl ketone. Thus, this serine proteinase appears to be a chymotrypsin-like enzyme and represents nearly 90% of the total extracellular azocasein-hydrolyzing activity produced by strain C5-A13. Since CaCO3 did not stimulate activity of the purified enzyme itself, the carbonate effect may be a transcriptional or translational rather than a post-translational one.