This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
Phospholamban is a protein leads to 
Select and explain. 
A. That increase interaction of calcium with myofilaments, B. That leads to sequestration of calcium in endoplasmic reticulum, C. That leads to sequestration of calcium by mitochondria, D. That activates Ca/Na pump
B: That leads to sequestration of calcium in endoplasmic reticulum
Answer: B: That leads to sequestration of calcium in endoplasmic reticulum 
Explanation: That leads to sequestration of Ca2+ in endoplasmic reticulum Phospholamban is a protein contained within the sarcoplasmic reticulum that inhibits the activity of the sarcoplasmic calcium pump. Inactivation of the phospholamban results in an increase in calcium sequestration by the SR. In cardiac muscle, the rapid sequestration of Ca2+ shoens the duration of the contraction. In smooth muscle, sequestration causes the muscles to relax. Phospholamban has little effect on skeletal muscle contraction.