ADENYLYL-CYCLASE ACTIVITY IN ROOTS OF PISUM-SATIVUM

An extract exhibiting adenylyl cyclase activity was obtained from root s of pea seedlings and the product of its incubation with ATP and Mg2 isolated and examined by tandem mass spectrometry. The data presented constitute the first unambiguous identification of the product of a p utative adenylyl cyclase from a higher plant source as adenosine 3',5' -cyclic monophosphate (cyclic AMP). A plot of reaction velocity agains t substrate concentration was sigmoidal, indicating allostery; 100 nM GTP activates the enzyme but 100 muM inhibits it. Inclusion of an ATP- regenerating system in the enzymic assay stimulated at the higher GTP concentration but not at the lower concentration. Possible effectors, including zeatin, gibberellin A3, indolylacetic acid and calmodulin we re examined; the results suggest that there is an additional, unidenti fied component of the enzymic system. The enzyme is associated with pa rticulate fractions.