Biochemistry If tyrosine level in blood is normal without external supplementation, deficiency of which of the following is ruled out ? A Tryptophan B Phenylalanine C Histidine D Isoleucine 💡 Explanation If tyrosine level in blood is normal without external supplementation, deficiency of which of the following is ruled out ? ✓ Correct Answer: B. Phenylalanine