The sarcoplasmic reticulum Ca^2+ ATPase (SERCA) pumps Ca^2+ out of the cytoplasm

Question

The sarcoplasmic reticulum Ca^2+ ATPase (SERCA) pumps Ca^2+ out of the cytoplasm and into the sarcoplasmic reticulum of muscle cells. Muscle contraction occurs in response to the rapid rise of Ca^2+ 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 Ca^2+ 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. 2 Ca^2+ bound 2 Ca^2+ and ADP bound P_i bound AMP bound ADP bound 2 Ca^2+, ATP bound 2 Ca^2+, ADP, and Pi bound

Explanation / Answer

For the active removal of Ca2+ ions, the transport mechanism involves binding of,

2Ca2+, ATP bound

Which creates a potential across cell and initiates fast removal of Ca2+.

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