Ref ID : 3874
Kudo Shuzo, Nakazawa Kinya, and Nozawa Yoshinori; Studies on Cyclic Nucleotide Metabolism in Tetrahymena pyriformis: Partial Characterization of Cyclic AMP- and Cyclic GMP-dependent Phosphodiesterases. J.Protozool. 27(3):342-345, 1980
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Cyclic nucleotide phosphodiesterase [E.C. 3.1.4.17] was examined in Tetrahymena pyriformis strain NT-1. Enzymic activity was associated with the soluble and the particulate fractions, whereas most of the cyclic GMP phosphodiesterase activity was localized in the soluble fraction; the activities were optimal, at pH 8.0-9.0. Although very low activities were detected in the absence of divalent cations, they were significantly increased by the addition of either Mg2+ or Mn2+. A kinetic analysis of the properties of the enzymes yielded 2 apparent Km values ranging in concentration from 0.5 to 50 µM and from 0.1 to 62 µM for cyclic AMP and GMP, respectively. A Ca2+ -dependent activating factor for cyclic nucleotide phosphodiesterase was extracted from Tetrahymena cells, but this factor did not stimulate guanylate cyclase [E.C. 4.6.1.2] activity in this organism. On the other hand, Tetrahymena also contained a protein activator which stimulated guanylate cyclase in the presence of Ca2+, although this activator did not stimulate the phosphodiesterase. The results suggested that Tetrahymena might contain 2 types of Ca2+ -dependent activators, one specific for phosphodiesterase and the other for guanylate cyclase.