Abstract
An extract exhibiting adenylyl cyclase activity was obtained from roots of pea seedlings and the product of its incubation with ATP and Mg 2+ 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 100μM 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 A 3, 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.
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