For calcium to be absorbed it must bind to a hormone regulated brush border protein called what

For calcium to be absorbed it must bind to a hormone regulated brush border protein called Calbindin.
Calbindins are calcium binding protein. As it names also shows that, Cal for calcium and bindin for binding. they are also described as vitamin D dependent calbindin proteins.
Calbindin-D9k and Calbindin-D28k are two identified forms of protein. 

When you are making a guess you are forming a hypothesis

Ther are many reasons.. is it a multiple choice?