OCCURRENCE OF NOVEL TYPES OF NITRIC-OXIDE SYNTHASE IN THE SILKWORM, BOMBYX-MORI

Nitric oxide (NO) synthase activity was detected in fat body and the M alpighian tubles of the silkworm, Bombyx mori. Main NO synthase activi ty in the fat body was Ca2+/calmodulin-dependent, inducible by bacteri al lipopolysaccharide (LPS) and required NADPH, FAD, FMN, dithiothreit ol (DTT) and tetrahydrobiopterin (BH4) as cofactors for the full expre ssion of the activity. The Malpighian tubles contained two types of NO synthase. One was Ca2+-independent, calmodulin-dependent and constitu tive and the other was Ca2+-dependent and constitutive. The former NO synthase required the same cofactors as fat body NO synthase. The acti vity of Malpighian tuble NO synthases increased dramatically at the en d of the last instar period, just prior to spinning. These results ind icate that B. mori contains new types of NO synthase, suggesting the w ide distribution and different characteristics of this enzyme among ve rtebrates and invertebrates. (C) 1995 Academic Press. Inc.