The cell can change the pH of its internal compartments using membrane transport proteins that pump protons into or out of a compartment. How many protons should be pumped into an endocytic vesicle that is 10-¹⁵ liters in volume and has a neutral pH in order to change the pH to 5? Avogadro's number is 6 × 10²³. Omit complications such as the membrane potential, buffers, and other cellular components.