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 [α-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.