ACa²⁺ - ATPase
BH⁺/K⁺ - ATPase
CH⁺ - ATPase
DH⁺ - PPase
Answer:
B. H⁺/K⁺ - ATPase
Read Explanation:
The electro-neutral pump - H⁺/K⁺ - ATPase.
Electroneutral vs. Electrogenic Pumps
An electrogenic pump generates an electrical potential across the membrane because it transports a net charge. For example, the Na⁺/K⁺ pump extrudes 3 positive sodium ions for every 2 positive potassium ions it imports, resulting in a net export of one positive charge per cycle. This contributes to the resting membrane potential.
An electroneutral pump does not generate an electrical potential because it exchanges an equal number of charges. The overall charge on both sides of the membrane remains balanced.
Ca²⁺ - ATPase: This pump, found in the plasma membrane (PMCA), is generally considered electroneutral. It extrudes one Ca²⁺ ion in exchange for two H⁺ ions, balancing the positive charges and preventing a net change in membrane potential.
H⁺/K⁺ - ATPase: This pump, particularly the one in the stomach, is electroneutral. It exchanges one H⁺ ion for one K⁺ ion. The transport of one positive charge out and one positive charge in results in no net charge movement across the membrane.
H⁺ - ATPase: These are typically electrogenic pumps. For example, the H⁺-ATPase found in the plasma membrane of plants, fungi, and some protists pumps a proton out of the cell without exchanging another ion. This creates a membrane potential.
H⁺ - PPase: This pump, which uses pyrophosphate for energy, is also electrogenic. It pumps H⁺ ions into organelles like the vacuole in plants, generating a positive potential inside the vacuole.
Given the options, both the Ca²⁺ - ATPase and H⁺/K⁺ - ATPase are electroneutral. However, the H⁺/K⁺ - ATPase is the classic and most commonly cited example of an electroneutral pump in a biological context. The Ca²⁺ - ATPase is also electroneutral. If the question implies a single correct answer, both A and B are plausible depending on the context of the course material.