Micromethods for Measuring Phenylalanine and Tyrosine in Serum

Abstract

Spectrophotofluorometric micromethods for the determination of phenylalanine and tyrosine on 25 µl of serum are described. These methods were applied to detect phenylketonuria among homozygotes and heterozygotes and in the newborn population. The data presented agree with those previously reported. (1) Phenylketonurics have markedly elevated serum phenylalanine and lower serum tyrosine than the controls. (2) The heterozygotes have a higher fasting serum phenylalanine and, after a standard oral phenylalanine test, show a higher and more prolonged rise of serum phenylalanine than the controls. There was a lesser increase of serum tyrosine after phenylalanine loading in the heterozygotes than the controls. (3) Premature infants of low birth weight have higher serum phenylalanine and tyrosine levels than normal birth weight infants, presumably due to enzyme immaturity. Simultaneous determinations of serum phenylalanine and tyrosine will differentiate newborn infants who are suspected to be phenylketonurics from the homozygotes (phenylketonurics).

Amino Acid Metabolism in Hereditary Fructosemia

“…Quantitative determination of serum phenylalanine and tyrosine was performed according to Wong et al (19). Amino acids were determined in serum, ascitic fluid and urine on a Technicon Amino Acid Autoanalyzer as previously described (16).…”

Acceleration of noradrenaline biosynthesis in the guinea‐pig vas deferens by potassium

“…The method of Wong, O'Flynn & Inonye (1964) (and see Udenfriend, 1962) was used with slight modifications. The volume of the tyrosine sample was changed from 20 ttl to 500 ttl and 500 yd instead of 200 ,jd of the 1-nitroso-2-naphthol-nitratenitrite reagent was added to the reaction mixture.…”

Genetic divergence in relatives of PKU's: Low IQ correlation among normal siblings

“…Verification of whether the siblings above 119 IQ were for the most part homozygotes requires accurate individual carrier tests. Unfortunately, all carrier tests presently available appear to have their competent detractors (Bremer & Neumann, 1966;Cunningham et al, 1969;Diachkova & Lebedev, 1969;Perry et a]., 1967;Rampini et al, 1969;Wong et al, 1964;Woolf et al, 1967).…”

“…Heterozygotes were reported to respond to loading with a distinctive curve of higher blood phenylalanine and a slower return to base level than normals (Hsia, Driscoll, Troll, & Knox, 1956), and with a more limited rise in blood tyrosine than normals (Anderson, Gravem, Ertel, & Fisch, 1962;Jervis, 1960). Subsequently, the differentiation between individual carriers and noncarriers has been questioned (Bremer & Neumann, 1966;Cunningham, Day, Berman, & Hsia, 1969;Diachkova & Lebedev, 1969;Perry, Tischler, Hansen, & MacDougall, 1967;Rampini, Anders, Curtius, & Marthaler, 1969;Wong, O'Flynn, & Inouye, 1964;Woolf, Cranston, & Goodwin, 1967).…”