Calmodulin is an ubiquitous cytoplasmic protein which mediates many of the actions of calcium on intestinal tissue including regulation of growth and differentiation of normal and neoplastic cells. Using a biotinylated calmodulin overlay system, we compared the pattern of calmodulin binding proteins throughout the gastrointestinal tract of mice, rats, rabbits, and humans, and in human colonic adenomas and adenocarcinomas. A common calmodulin binding protein of 67 kDa was found in membrane and cytosolic fractions of oesophagus, stomach, proximal and distal small intestine, and colon from all four species. In human tissue this 67 kDa protein was present in greatest concentration in stomach tissue. Furthermore, a 67 kDa binding protein was the major calmodulin binding protein from human stomach and ileum as determined by ion exchange and calmodulin affinity chromatography. A similar pattern of binding proteins was noted between rabbit and human cytosolic fractions; proteins of 60/67 kDa and 105 kDa were present in stomach tissue. A 94 kDa protein was present in samples of rabbit and human ileum but not of mouse or rat. A similar pattern of calmodulin binding proteins was seen in normal and neoplastic large bowel tissue, apart from one of nine adenocarcinomas, where a distinct 54 kDa band was noted in both cytosolic and membrane fractions. The results of this study show interspecies and organ differences between calmodulin binding proteins, but suggest that a 67 kDa protein is the major binding protein present throughout normal gastrointestinal tract and neoplastic human tissue.
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