Along with the general pathways of amino acid metabolism, some amino acids also have their specific metabolic pathways. Impaired metabolism of a certain amino acid can result in decreased synthesis of melanin, catecholamines, and thyroid hormones. Name this amino acid.

• A. Sulfur-containing amino acids
• B. Histidine
• C. Valine, leucine, isoleucine
• D. Phenylalanine
• E. Tryptophan