Adenylyl cyclase activity in roots of Pisum sativum

An extract exhibiting adenylyl cyclase activity was obtained from roots 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 putative adenylyl cyclase from a higher plant source as adenosine 3',5'-cyclic monophosphate (cyclic AMP). A plot of reaction velocity against 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 were examined; the results suggest that there is an additional, unidentified component of the enzymic system. The enzyme is associated with particulate fractions.