The major intracellular anion is phosphate (PO₄³⁻).

Here's why:

* Phosphate's Role: Phosphate is involved in many essential cellular processes, including:

* Energy storage and transfer (ATP)

* DNA and RNA structure

* Cell signaling

* Buffering pH

* Proteins: While proteins are negatively charged at physiological pH, their concentration within cells is generally lower than phosphate.

* Other Anions: Other important intracellular anions include bicarbonate (HCO₃⁻) and chloride (Cl⁻), but phosphate typically holds the highest concentration.

Therefore, although proteins contribute to the overall negative charge inside cells, phosphate is the dominant intracellular anion.