Question

The sarcoplasmic reticulum Ca2 ATPase (SERCA) pumps Ca2 out of the cytoplasm and into the sarcoplasmic reticulum of muscle cells. Muscle contraction occurs in response to the rapid rise of Ca2 in the cytoplasm. Calcium ions must be removed form the cytoplasm for muscle relaxation to occur. SERCA removes the calcium ions, enabling muscle relaxation. SERCA is a monomeric protein with a nucleotide-binding domain (N), a domain that accepts a phosphoryl group (P), and an actuator domain (A). A transmembrane domain binds calcium ions.

From what you know of the mechanism of Ca2 transport, which of the following binding patterns are observed at any point? Select all that apply. Assume that only the species mentioned are bound. For example, if ADP is not mentioned, it is not bound.

Select all that apply. (Four correct answers)

2 Ca2 , ADP, and Pi bound

ADP bound

2 Ca2 and Pi bound

AMP bound

2 Ca2 bound

Pi bound

2 Ca2 , ATP bound

Answer 1