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Regulation of in vivo phenylalanine hydroxylation by dietary tyrosine using enrichment in Apo‐B100
Author(s) -
Rafii Mahroukh,
McKenzie Jane M,
Roberts Susan A,
Steiner George,
Ball Ronald O,
Pencharz Paul B
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a332
Subject(s) - phenylalanine , tyrosine , hydroxylation , chemistry , apolipoprotein b , phenylalanine hydroxylase , endocrinology , medicine , amino acid , in vivo , biochemistry , biology , enzyme , cholesterol , microbiology and biotechnology
We compared estimates of phenylalanine hydroxylation (Phe‐OH), across a range of tyrosine intakes, determined using plasma and ApoB‐100 phenylalanine and tyrosine enrichments, with a measurement of in vivo change in protein synthesis. Six, healthy, male subjects receiving 4.54 μmol.kg −1 .h −1 of phenylalanine, were randomized to receive each of the 7 test tyrosine intakes (3, 4.5, 6.0, 7.5, 9.0, 10.5 and 12 mg.kg − 1.d −1 ) for 3‐d. Studies were conducted at each level using the tracers of L‐[15N] phenylalanine and L‐[3,3‐2H2] tyrosine. Blood samples were collected at baseline and isotopic steady state. Repeated ANOVA using mixed model was performed to assess the effect of tyrosine intake on phenylalanine hydroxylation. Using ApoB‐100 as the sampling site, estimates of phenylalanine hydroxylation were lower than those from plasma phenylalanine and tyrosine. Apob‐100 enrichment followed a linear plateau pattern with a break point at a tyrosine intake of 6.8 mg.kg −1 .d −1 . We conclude that ApoB‐100 is a more suitable method than plasma for estimating intracellular enrichment of amino acids in the liver. (CIHR supported). 1 Effect of Tyrosine intake on Phe‐OH (μmol.kg −1 .h −1 ) in plasma and ApoB‐100 protein