Preparation and Use of Iodinated Calmodulin for Studies of Calmodulin-binding Proteins

A modification of calmodulin that has been particularly useful in studies of calmodulin and its role in the cell is iodination. Iodination of calmodulin has been employed to establish radioimmunoassays to detect and measure calmodulin in biological tissues. Iodination of calmodulin under carefully controlled conditions also allows the introduction of an isotopic label with retention of drug binding, protein binding, and enzyme activator properties. This chapter summarizes some observations that are important for the reproducible use of iodinated calmodulin in studies of calmodulin-binding proteins and calmodulin activator activities. Vertebrate calmodulin can be readily iodinated by methods utilizing chloramine-T, lactoperoxidase, or Bolton-Hunter reagent. The chapter shows the results obtained when a partially purified bovine brain phosphodiesterase preparation and purified chicken gizzard myosin light-chain kinase were tested for their ability to interact with iodinated calmodulin. The results are consistent with the phosphodiesterase activator assays.