IMMUNOLOGICAL ANALYSIS OF DEVELOPMENTAL-CHANGES IN ECDYSONE 20-MONO-OXYGENASE EXPRESSION IN THE COTTON LEAFWORM, SPODOPTERA-LITTORALIS

The developmental changes in ecdysone 20-mono-oxygenase during the six th larval instar of the cotton leafworm, Sponoptera littoralis, were i nvestigated. The specific activity of mitochondrial ecdysone 20-mono-o xygenase in the fat-body exhibited a distinct peak at 72 h, at which t ime the larvae stop feeding. Immunoblot analyses, using antibodies rai sed against components of vertebrate mitochondrial steroidogenic enzym e systems [anti-(cytochrome P-450(scc)), anti-(cytochrome P-450(11 bet a)), anti-adrenodoxin and anti-(adrenodoxin reductase) antibodies], re vealed the presence of specific immunoreactive polypeptides in fat-bod y mitochondrial extracts. In addition, these antibodies effectively in hibited fat-body mitochondrial ecdysone 20-mono-oxygenase activity. Th is suggests that the S. littoralis steroid-hydroxylating system(s) may contain polypeptide components analogous to those present in vertebra tes. A dose correlation between developmental changes in mitochondrial ecdysone 20-mono-oxygenase activity and the abundance of polypeptides (approx. 66 kDa and 50 kDa) recognized by the anti-(cytochrome P450(1 1 beta)) antibody and a polypeptide (approx. 52 kDa) recognized by the anti-(adrenodoxin reductase) antibody were observed in both fat-body and midgut. These results suggest that developmental changes in the ab undance of components of the ecdysone 20-mono-oxygenase system may pla y an important role in the developmental regulation of the enzyme expr ession and, hence, of 20-hydroxyecdysone titre.