Characterization of Cyclic Nucleotide Phosphodiesterase Activity in Sunflower Callus

Abstract

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.

Induction of an Extracellular Cyclic Nucleotide Phosphodiesterase as an Accessory Ribonucleolytic Activity during Phosphate Starvation of Cultured Tomato Cells

“…Intriguingly, characteristics of the second class of plant cyclic nucleotide phosphodiesterases suggest a function in RNA degradation, which was first proposed by Lin and Varner (1972). Therefore, it is not surprising that tomato extracellular cyclic nucleotide phosphodiesterase shares several key characteristics with preparations of phosphodiesterases from pea (Lin and Varner, 1972), barley (Vandepeute et al, 1973), potato (Ashton and Polya, 1975;Zan-Kowalczewska et al, 1984), sunflower (Junker et al, 1977), spinach (Brown et al, 1980), lettuce (Chiatante et al, 1988), or Lemna (Gangwani et al, 1994, such as molecular mass of the monomer unit (65-80 kD), an acidic pH optimum (pH 5-7), lack of requirement for bivalent metal ions, and broad substrate specificity. In general, higher plant cyclic nucleotide phosphodiesterases of this class hydrolyze, irrespective of the nucleobase present, 2Ј:3Ј-cyclic NMP to 3Ј-NMP at a higher rate than 3Ј:5Ј-cyclic NMP to a mixture of 3Ј-NMP and 5Ј-NMP, typically in a ratio of 7 to 1 (Lin and Varner, 1972), which is similar to the ratio observed for the tomato enzyme (6:1).…”

“…3.1.4.37), forming 2Ј-NMP products, and may function in tRNA splicing (Culver et al, 1994), or in unknown biological processes. Physical and catalytic properties of the tomato extracellular phosphodiesterase are markedly different from members of this class, but are strikingly similar to enzymes that have been studied during efforts to identify 3Ј:5Ј-cAMP phosphodiesterase activity as indirect evidence for the presence and function of 3Ј:5Ј-cAMP in plants (Lin and Varner, 1972;Vandepeute et al, 1973;Ashton and Polya, 1975;Brown et al, 1977;Junker et al, 1977Junker et al, , 1979Junker et al, , 1980Zan-Kowalczewska et al, 1984;Dupon et al, 1987;Chiatante et al, 1988;Gangwani et al, 1994). However, properties of most plant cyclic nucleotide phosphodiesterases characterized during those investigations have been found to differ significantly from animal and bacterial 3Ј:5Ј-cyclic nucleotide-3Ј-phosphodiesterases.…”

Adenosine 3′:5′‐Cyclic Monophosphate in Normal and Habituated Helianthus Callus

“…The PDE preparation might contain impurities which can demobilize other compounds than cAMP active in the Gilman assay (Lin 1974, Amrhein 1977. The PDE in Helianthus callus also lacks an absolute specificity for cAMP (Junker et al 1977).…”

Characterization of cyclic nucleotide phosphodiesterase activity in Phaseolus vulgaris

“…Several reports of cyclic nudeotide phosphodiesterase activity in higher plant tissues have been published (Niles and Mount 1974, Junker et al 1977, Smeltzer and Johnson 1977, Brown et al 1977, 1979. In general these plant enzymes are distinct in one or tnore respects from their animal counterparts.…”