K-254-I (Genistein), a New Inhibitor of Ca²⁺ and Calmodulin-Dependent Cyclic Nucleotide Phosphodiesterase from Streptosporangium vulgare

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A new calmodulin antagonist, genistein, was isolated from the culture broth of Streptosporangium vulgare K-254. The spectral data of K-254-I indicated that the compound was identical with genistein, 4', 5, 7-trihydroxyisoflavone. Genistein inhibited the Ca²⁺/calmodulin-dependent activity of cyclic nucleotide phosphodiesterase from bovine brain (IC₅₀=20μM) without appreciably affecting its basal activity. The inhibitory activity of genistein was antagonized by higher concentrations of calmodulin. Although phosphatidylserine did not reverse the inhibition of calmodulin, genistein inhibited the phospholipid-sensitive, Ca²⁺-dependent protein kinase (protein kinase C) from bovine brain (IC₅₀=35.3μM). The activity of cAMP-dependent protein kinase was not affected by 700μM of genistein.