Pulses of red light initially increase the amount of cyclic AMP in Evernia prunastri thalli although with successive light treatments, nucleotide concentration was restored to its initial value. This enhancing effect is not photoreversible, since the amounts of cyclic AMP are even higher when far-red light pulses followed red light. This situation is not reversed by theophylline (an inhibitor of phosphodiesterase) or forskoline (an activator of adenylate cyclase). However, photoreversibility is found when EDTA presumably inhibits both phosphodiesterase and protein kinase.
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