Occurrence and Potential Ecological Significance of Cyclic Nucleotide Phosphodiesterase in Epilimnetic Lake
Abstract
Particulate-associated (15-60 nmol 1-1 h-1) and extracellular (15-25 nmol 1-1 min-1) cyclic nucleotide phosphodiesterase (cPDE) activity was identified in epilimnetic waters from a eutrophic reservoir. The pH optima (7.0-8.0), temperature optima (30-35� C), substrate specificity, and rnethylxanthine sensitivity of lakewater cPDE isolates paralleled characteristics of known animal cell and algal cPDE. Particulate cPDE appeared to be a surface-associated exoenzyme, rather than an intracellular enzyme. Simultaneous measurements of particulate and filtrate cAMP concentrations coupled with cPDE assays suggested that cPDE hydrolysis represented the major pathway of dis~olved cAMP turnover in this system.
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