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.