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. Author manuscript; available in PMC: 2013 Aug 1.
Published in final edited form as: J Acad Nutr Diet. 2012 Aug;112(8):1201–1210. doi: 10.1016/j.jand.2012.05.004

Figure 1.

Figure 1

Phenylalanine (phe) metabolism in phenylketonuria (PKU). As indicated by the “X”, PKU results from mutations (over 600 have been identified) that typically affect the hepatic phe hydroxylase enzyme needed for the hydroxylation of the dietary indispensable amino acid phe to tyrosine. PKU may also result from mutations in the recycling of the essential cofactor tetrahydrobiopterin. Due to these mutations which reduce the conversion of phe to tyrosine, phe accumulates in blood and is transaminated and decarboxylated into many compounds which appear in blood and urine; three of the compounds which are measured clinically are shown. Tyrosine, a precursor for multiple biological products, becomes an indispensable AA and must be provided by the diet for those with PKU.