Regulatory properties of adenylate cyclase preparations of pharate adult from the insect Ceratitis capitata

Abstract

1. 1. Adenylate cyclase from the pharate adult stage of development of the insect Ceratitis capitata is a membrane-bound Me 2+-dependent enzyme. Mn 2+ was more effective in promoting the catalytic activity of the enzyme than Mg 2+. Calcium ions inhibited the enzyme activity in the presence of either Mg 2+ or Mn 2+. 2. 2. Activation of the enzyme by fluoride in the presence of Mg 2+ was higher than in the presence of Mn 2+. The presence of fluoride did not modify the affinity of the enzyme to the substrate but V max was increased. 3. 3. Regulatory properties of this enzyme from the insect pharate adult were different from those of adenylate cyclase from adult brain membranes. 4. 4. Thus, GTP increased slightly the Mg 2+-basal activity whereas it inhibited the Mn 2+-basal activity. 5. 5. GppNHp activated markedly the Mg 2+-basal activity; however, GppNHp in the presence of Mn 2+ exerted a dual effect, activation and inhibition, at low and high nucleotide concentrations, respectively. 6. 6. Octopamine did not affect the GTP-dependent enzyme activity, possibly due to the low presence of nervous system in the pharate adult stage of development.