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Characterization of Cyclic Nucleotide Phosphodiesterase Activity in Sunflower Callus
- JUNKER, S., VERBEEK‐WYNDAELE, R., TRUELSEN, T.A.
- Physiologia plantarum 1977 pp. 45-50
- Helianthus annuus, adenosine monophosphate, adenosine triphosphate, caffeine, callus, cyclic AMP, enzyme activity, enzymes, metal ions, pH, plant age, plant growth substances, sodium fluoride, theophylline
- A membrane‐bound and a soluble cyclic nucleotide phosphodiesterase from sunflower callus has been examined. Kinetic studies showed Km‐values in the range of 2.5‐5.0 mM with cyclic adenosine 3′,5′‐monophosphate (3′, 5′‐cAMP) as the substrate. The soluble cyclic nucleotide phosphodiesterase was characterized further: Optimal activity was at pH 6.5‐7.0 and at 40°C. The enzyme did not require divalent metal ions for maximal activity. It was inhibited by Cu²⁺ and slightly activated by Fe³⁺. Sodium fluoride, imidazole and theophylline did not affect the activity, but caffeine was slightly inhibitory. Its activity was strongly inhibited by ATP, AMP and Pi. The enzyme hydrolysed 3′,5′‐cAMP, 2′,3′‐cAMP and 3′,5′‐cGMP, while N⁶, O²′‐dibutyryl cyclic AMP (dBcAMP) was left unattacked. The soluble enzyme activity was influenced neither by callus age nor by plant growth substances added in vivo or in vitro.