Identification and primary structure of a calbindin 9K binding domain in the plasma membrane Ca²⁺pump

Bovine calbindin 9K has been conjugated to a bifunctional, photoactivatable, cleavable and radioactive cross-linker. It has been photolyzed in the presence of preparations of the purified crythrocyte Ca²⁺ pump, and shown to interact with it in the presence of Ca²⁺. The affinity of the interaction has been studied using the fluorescence enhancement of dansylated calbindin 9K incubated with the synthetic calmodulin binding domain of the pump. Two versions of the domain have been used, one corresponding to its full length (28 residues), one to about of it (20 residues). The affinity of the interaction was between 5 and 10 times lower than in the case of calmodulin.