Sensitive in vivo assay of the phenylalanine hydroxylating system with a small intravenous dose of heptadeutero L-phenylalanine using high pressure liquid chromatography and capillary gas chromatography/mass fragmentography.
A method is described which allows the in vivo determination of the phenylalanine hydroxylating system in atypical and classical phenylketonuria. Phenylalanine-d7 is administered i.v. (0.030 g/kg body weight) within 10 min. Tyrosine-d6 in plasma is measured from 30 to 240 min post load by using a computerized capillary gas chromatography/mass fragmentography system. In two patients with hyperphenylalaninemia, the residual activity of the phenylalanine hydroxylating system was 15.7 and 3.7% of the normal, in two phenylketonurics 1.5 and 0.3% respectively. The in vivo figures correspond well to the in vitro assay of the residual activity of the phenylalanine hydroxylase in needle liver biopsy material.
D000328:Adult; D000592:Amino Acid Metabolism, Inborn Errors / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003903:Deuterium; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D007223:Infant; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D010649:Phenylalanine / Q000378:metabolism; D010651:Phenylalanine Hydroxylase / Q000172:deficiency / Q000378:metabolism*; D010661:Phenylketonurias / Q000201:enzymology*
D010649:Phenylalanine; D003903:Deuterium; D010651:Phenylalanine Hydroxylase