UNUSUAL PROTEOLYTIC PROCESSING OF A DELTA-ENDOTOXIN FROM BACILLUS-THURINGIENSIS STRAIN BUIBUI BY LARVAL MIDGUT-JUICE OF ANOMALA-CUPREA HOPE(COLEOPTERA, SCARABAEIDAE)

The coleopteran-active delta-endotoxin of Bacillus thuringiensis serov ar japonensis strain Buibui had a so-called proteinase-resistant regio n of 50 kDa which is resistant to trypsin and larval midgut-juice of B ombyx mori. However, the delta-endotoxin of strain Buibui was degraded to smaller polypeptides of less than 20 kDa by larval midgut-juice of Anomala cuprea. In addition, the CryIAa delta-endotoxin was also degr aded to smaller polypeptides by the midgut-juice. On the other hand, a mixture of trypsin and autoclaved A. cuprea midgut-juice degraded the delta-endotoxin to smaller polypeptides but the autoclaved midgut-jui ce with Staphylococcus aureus V8 proteinase or lysyl endopeptidase did not. These results suggest that A. cuprea midgut-juice may have a hig h activity to digest the delta-endotoxins, for which a trypsin-like pr oteinase may play an important role. Moreover, A. cuprea midgut-juice may contain a factor(s) which cooperates with trypsin to digest delta- endotoxin into smaller polypeptides.