Energy transduction in quinone inhibition of insect feeding

Variously substituted 1,4-naphthoquinones inhibited (deterred) feeding by Periplaneta americana. Certain sensilla on the antennae were important receptors for the deterrent stimulus. Dendritic branches of sensory neurons in the sensilla are exposed to the exogenous inhibitory chemicals via pores which penetrate the cuticle. The order of relative degree of complexing of a given naphthoquinone to density-gradient fractions of antennal homogenates rich in nerve membrane fragments matched the order of relative deterrency of that chemical to feeding. Sulphhydryl groups of protein in the antennae were important sites of reaction. Energy transduction at the receptor site involved complexing of the quinone with the receptor chemical and the ultimate reduction of the quinone to its quinol. Energy transfer between sulphhydryl groups and quinones provided a mechanism which could bring about a change in conformation of the receptor macromolecule which could allow inorganic ion flows to generate the action potential of the neuron.