Biochemistry The most impoant factor controlling the rate of mitochondrial oxidative phosphorylation is the: A Concentration of inorganic phosphate. B Concentration of O2. C Number of protons pumped. D Level of ADP. 💡 Explanation The most impoant factor controlling the rate of mitochondrial oxidative phosphorylation is the: ✓ Correct Answer: D. Level of ADP.