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One of the essential amino acids, present in many common proteins, especially hemoglobin. It is used in medicine and nutrition and as one of the two amino acids making up aspartame. Persons with phenylketonuria do not metabolize phenylalanine properly and must adhere to a diet free of it.
This entry comes from Encyclopædia Britannica Concise. For the full entry on phenylalanine, visit Britannica.com.