ADENYLATE AND GUANYLATE CYCLASES OF CECROPIA SILKMOTH FAT-BODY

Adenylate and guanylate cyclases were assayed in silkmoth fat body homogenates by measuring the conversion of [.alpha.-32P]nucleoside triphosphates to cyclic [32P]nucleotides. Adenylate cyclase was dependent on dithiothreitol, required either Mg2+ or Mn2+ for activity, was activated by NaF and inhibited by Triton X-100. Guanylate cyclase was not dependent on dithiothreitol, was strictly dependent upon Mn2+, unaffected by NaF and activated by Triton X-100. Both cyclases had pH optima near 8.0 and were located chiefly in the particulate fraction of homogenates. Activities of both cyclases were maintained or elevated during the larval-pupal transformation and, in contrast to cyclic nucleotide phosphodiesterases, showed little decline in the early diapausing pupa.