The plasmodium of the myxomycete Physarum flavicomum secretes cyclic AMP phosphodiesterase into the medium. The extracellular enzyme had a pH optimum between 7 and 8 and a Km of about 500 μM cyclic AMP and was inhibited by theophylline, caffeine and 3-isobutyl-l-methyxanthine (MIX). A marked decrease of enzyme activity was noted in the presence of EDTA, suggesting the requirement of Mg+ + by the enzyme. Addition of Mg+ + and Ca + + stimulated the enzyme while Zn+ + , Co+ + , Pb+ + , Mn+ + , Fe + + + , Ni+ + , and Cu + + all inhibited phosphodiesterase activity. An interesting feature of this extracellular phosphodiesterase was its ability to retain full catalytic activity after prolonged exposure to elevated temperatures
Lynch, Thomas J. and Farrell, Mary E.
"Extracellular Phosphodiesterase from the Growth Medium of the Myxomycete Physarum flavicomum,"
Journal of the Arkansas Academy of Science: Vol. 38
, Article 17.
Available at: http://scholarworks.uark.edu/jaas/vol38/iss1/17