Stimulation of diamondback moth ( Plutella xylostella) adenylate cyclase activity by a carbodiimide

Abstract

1. DFCD or 3-(2,6-diisopropyl-4-phenoxyphenyl)-1- tert-butylcarbodiimide, a toxic metabolite of the thiourea acaricide/insecticide diafenthiuron, stimulated adenylate cyclase activity in preparations from heads of adult diamondback moths, Ptutella xylostella (L.). 2. Depending upon assay conditions, DFCD gave a biphasic response with K a, values of 0.025 and 1.25 μM for high and low affinity components, respectively, or a monophasic response with a K a of 0.4 μM. 3. Studies with potential agonists and antagonists suggested that octopamine-sensitive ( K a 7.5 μM) and dopamine-sensitive ( K a, 1.0 μM) adenylate cyclases were present. 4. At maximally effective concentrations, the activity of DFCD was nonadditive to that of octopamine or dopamine. 5. It appeared that DFCD was binding to octopamine- and dopamine-sensitive adenylate cyclases and that affinity of the carbodiimide was higher for the former than for the latter. 6. These actions on biogenic amine-sensitive adenylate cyclases likely are involved in the toxicity of diafenthiuron to diamondback moths.