We have previously reported that the actin gelation inhibitor, derived from platelets is a protein of MW 90, 000.
By affinity chromatogaphy in the presence of 0.1mM CaCl2, a protein of MW 20, 000 was obtained in addition to the gelation inhibitor (MW 90, 000) and actin (MW 45, 000). As the protein of MW 20, 000 was gel-electrophoresised in accordance with brain calmodulin in the presence of EGTA or CaCl2, it was thought to be calmodulin. But in the presence of CaCl2, the brain calmodulin could not activate the gelation inhibitor activity. On the other hand when, in the presence of EGTA, the sample containg the gelation inhibitor was mixed with [3H] calmodulin and then chromatographied by Sephacryl S-200gel filtration, the radioactivity of the isotope of calmodulin was detected in accordance with the protein peak of the sample. These results suggest the possibility that the actin gelation inhibitor binds to calmodulin in the presence of EGTA, not in the presence of CaCl2.