Purification and characterization of calcium-calmodulin kinase II from human parathyroid glands

Calmodulin has been identified in parathyroid cells and is thought to play an important role in the production or secretion of parathyroid hormone. However, a detailed investigation of calmodulin-binding proteins in parathyroid glands has not been conducted. In this study, we attempted to determine the presence of calmodulin-binding protein in human parathyroid adenoma by affinity chromatography. The eluted protein from a calmodulin-coupled Sepharose 4B column with EGTA was analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis which revealed a major protein band of Mr 50,000. A Ca2+/calmodulin-dependent protein kinase activity was detected at the protein peak using dephosphorylated casein as a substrate. The 50 kDa band was identified as calcium/calmodulin-dependent protein kinase II (CaM-kinase II) by immunoblotting. The substrate specificity, pH dependency and affinity for calmodulin of this enzyme were identical to those of CaM-kinase II from rat brain. Also, the kinase activity was sensitive to KN-62, a specific inhibitor of CaM-kinase II. In total, 0.48 mg of this kinase was purified from 3 g human parathyroid adenoma.