Enzymatic cycling assay for phenylpyruvate

Enzymatic cycling assays for the determination of L-phenylalanine and phenylpyruvate in deproteinized tissue extracts are described. Assay 1 couples glutamine transaminase K with L-phenylalanine dehydrogenase. Assay 2 combines phenylalanine dehydrogenase, L-amino acid oxidase, and catalase. In both assays, tyrosine and some other amino acids (or their alpha-keto acid analogs) can replace phenylalanine (or phenylpyruvate) to a small extent. Thus, if phenylalanine is to be measured a correction must be made for the nonspecificity of the reaction. By removing phenylalanine on a cation-exchange column it was possible to measure phenylpyruvate in tissue extracts. Concentrations of phenylpyruvate (mumol/kg) in normal rat liver, kidney, and brain were 2.1 +/- 1.1 (n = 8), 1.8 +/- 0.4 (n = 4), and 3.3 +/- 0.6 (n = 4), respectively.

Blood phenylalanine estimation for the patient with phenylketonuria using a portable device

A simple and reliable method is described which is suitable for estimation of a whole blood phenylalanine concentration for the patient with PKU in various settings including the physician's office and the home. Excellent correlations were obtained between this method and weighed phenylalanine standards, as well as with measurement of phenylalanine in serum, plasma, and whole blood, using the McCaman-Robins fluorometric assay. Increasing the frequency and rapidity of feedback to the patient should improve metabolic control, just as home glucose monitoring has for the patient with diabetes mellitus. This method is immediately adaptable to monitoring patients with tyrosinemia, and with substitution of the appropriate amino acid ammonia lyase could be used for other amino acidemias.