Bovine taste bud cyclic adenosine 3', 5' monophosphate phosphodiesterase is inhibited by divalent metal ions

Two fractions from bovine taste buds, the soluble S4 fraction and the membrane P4B fraction, were used to evaluate the effects of divalent metal ions on cyclic adenosine 3', 5' monophosphate (cAMP) phosphodiesterase (PDE) activity. Zn++, Ni++, Cu++, Fe++, Sn++ and Hg++, in the presence of 5mM Mg++, inhibited cAMP PDE activity whereas these divalent metal ions alone did not affect enzyme activity if Mg++ were absent. Zn++ inhibited cAMP PDE activity in S4 and P4B taste bud fractions with Ki values of 100 microM and 90 microM, respectively; this inhibition was noncompetitive with substrate activity but competitive with Mg++. In the presence of Mg++, Zn++ inhibited taste bud cAMP PDE more effectively than any other metal ion studied. Inhibition of taste bud cAMP PDE by divalent metal ions, particularly Zn++, suggests a role for these substances in the taste process through regulation of intracellular concentration of taste bud cAMP.