This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
The function of Phospholamban is 
Select and explain. 
A. Regulates Na+ K+ pump, B. Transports calcium out of the mitrochondria, C. Binds actin with myosin, D. Inhibits Ca++ pump on sarcoplasmic reticulum
D: Inhibits Ca++ pump on sarcoplasmic reticulum
Answer: D: Inhibits Ca++ pump on sarcoplasmic reticulum 
Explanation: Phospholamban inhibits calcium pump on sarcoplasmic reticulum, thereby preventing uptake of Ca++ from the sarcoplasm. 
When it is phosphorylated, the Ca++ channels open up and uptake of Ca++ is increased into the sarcoplasmic reticulum.