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dc.contributor.authorRafii, M.
dc.contributor.authorMcKenzie, Jane
dc.contributor.authorRoberts, S. A.
dc.contributor.authorSteiner, G.
dc.contributor.authorBall, R. O.
dc.contributor.authorPencharz, P. B.
dc.date.accessioned2018-06-29T21:33:06Z
dc.date.available2018-06-29T21:33:06Z
dc.date.issued2008-02
dc.identifierER770
dc.identifier.citationRafii, M., McKenzie, J., Roberts, S., Steiner, G., Ball, R. & Pencharz, P. (2008) In vivo regulation of phenylalanine hydroxylation to tyrosine, studied using enrichment in apoB-100, AJP: Endocrinology and Metabolism, vol. 294, , pp. E475-E479,
dc.identifier.issn0193-1849
dc.identifier.urihttp://dx.doi.org/10.1152/ajpendo.00604.2007
dc.identifier.urihttps://eresearch.qmu.ac.uk/handle/20.500.12289/770
dc.description.abstractPhenylalanine hydroxylation is necessary for the conversion of phenylalanine to tyrosine and disposal of excess phenylalanine. Studies of in vivo regulation of phenylalanine hydroxylation suffer from the lack of a method to determine intrahepatocyte enrichment of phenylalanine and tyrosine. apoB-100, a hepatic export protein, is synthesized from intrahepatocyte amino acids. We designed an in vivo multi-isotope study, [15N]phenylalanine and [2H2]tyrosine to determine rates of phenylalanine hydroxylation from plasma enrichments in free amino acids and apoB-100. For independent verification of apoB-100 as a reflection of enrichment in the intrahepatocyte pool, [1-13C]lysine was used as an indicator amino acid (IAA) to measure in vivo changes in protein synthesis in response to tyrosine supplementation. Adult men (n = 6) were fed an amino acid-based diet with low phenylalanine (9 mgkg-1day-1, 4.54 _molkg-1,h-1) and seven graded intakes of tyrosine from 2.5 (deficient) to 12.5 (excess) mgkg -1day-1. Gas chromatography-quadrupole mass spectrometry did not detect any tracer in apoB-100 tyrosine. A new and more sensitive method to measure label enrichment in proteins using isotope ratio mass spectrometry demonstrated that phenylalanine hydroxylation measured in apoB-100 decreased linearly in response to increasing tyrosine intake and reached a break point at 6.8 mgkg-1day-1. IAA oxidation decreased with increased tyrosine intake and reached a break point at 6.0 mgkg-1day-1. We conclude: apoB-100 is an accurate and useful measure of changes in phenylalanine hydroxylation; the synthesis of tyrosine via phenylalanine hydroxylation is regulated to meet the needs for protein synthesis; and that plasma phenylalanine does not reflect changes in protein synthesis. Copyright 2008 the American Physiological Society.
dc.format.extentE475-E479
dc.relation.ispartofAJP: Endocrinology and Metabolism
dc.subjectApolipoprotein B-100
dc.titleIn vivo regulation of phenylalanine hydroxylation to tyrosine, studied using enrichment in apoB-100
dc.typearticle
dcterms.accessRightsrestricted
dc.description.facultysch_die
dc.description.volume294
dc.identifier.doihttp://doi:10.1152/ajpendo.00604.2007
dc.description.ispublishedpub
dc.description.eprintid770
rioxxterms.typearticle
qmu.authorMcKenzie, Jane
dc.description.statuspub
dc.description.number2


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