Inhibition of calmodulin-activated cyclic nucleotide phosphodiesterase by triton x-100

The activity of calmodulin-activated cyclic nucleotide phosphodies-terase in a standard reaction containing 40 ng calmodulin could be inhibited about 50% by 14 μM Triton x-100. In contrast, the calmodulin-independent phosphodiesterase required a much higher concentration of the detergent, 380 μM for 50% inhibition of its activity. The potent inhibitory effect of Triton X-100 on the calmodulin-activated phosphodiesterase reaction could be reversed by high concentrations of calmodulin. Using the gel filtration technique, it was demonstrated that ³H-Triton X-100 bound to calmodulin with high affinity in buffer containing Ca²⁺. The binding of the detergent to calmodulin was mostly eliminated in the presence of trifluoperazine, a neuroleptic drug. Among other detergents examined, including Lubrol WX, Triton QS and Triton CF, only Triton CF exhibited preferential inhibition of the calmodulin-activated phosphodiesterase. The results suggest that certain detergents in the Triton family inhibit calmodulin action by undergoing Ca²⁺-dependent binding to the protein at the neuroleptic drug site.