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A highly sensitive method for the determination of alpha-keto acids including phenylpyruvic acid in human plasma is investigated. The method employs high-performance liquid chromatography with chemiluminescence detection. The acids and alpha-ketocaproic acid (internal standard) in human plasma are isolated by anion-exchange chromatography on a Toyopak DEAE cartridge, and then converted into the corresponding chemiluminescent derivatives with 4,5-diaminophthalhydrazide dihydrochloride, a chemiluminescence derivatization reagent for alpha-keto acids. The derivatives are separated within 50 min on a reversed-phase column, TSKgel ODS-120T, with isocratic elution, followed by chemiluminescence detection; the chemiluminescence is produced by the reaction of the derivatives with hydrogen peroxide in the presence of potassium hexacyanoferrate(III). The detection limits for the acids are in the range 9-92 pmol/ml in plasma (signal-to-noise ratio = 3). This sensitivity permits precise determination of several alpha-keto acids including phenylpyruvic acid, which cannot be determined by other HPLC methods, in 10 microliters of normal human plasma. The chemiluminescent product from phenylpyruvic acid was characterized as 3-benzyl-7,8-dihydropyridazino[4,5-g]quinoxaline-2,6,9(1H)-trione.
Purified bovine liver branched chain ketoacid dehydrogenase is inhibited by its reaction products, NADH and the branched chain acyl-CoA thiol esters. This provides an immediate, short term regulation mechanism for this enzyme which commits leucine, isoleucine, and valine to the catabolic pathway. We find that clofibric acid (p-chlorophenoxymethylpropionic acid) and phenylpyruvate also specifically inhibit this multienzyme complex. Fifty percent inhibition occurs at 0.24 mM and 0.40 mM concentrations, respectively. Both compounds bind either free enzyme (E) or the enzyme-substrate (ES) complex to give an abortive enzyme-substrate-inhibitor (ESI) complex. Phenylpyruvate preferentially binds E (Ki = 48 microM) over ES (alpha Ki = 97 microM), while clofibric acid has a reverse preference, binding ES (alpha Ki = 48 microM) with more avidity than E (Ki = 142 microM). Amino acids like L-leucine, beta-leucine, and 2-aminonorbornyl-2-carboxylic acid do not inhibit this enzyme at concentrations as high as 10 mM. These biochemical probes will be useful for studying the catalytic site of this enzyme complex and the consequences of accumulated branched chain ketoacids and their amino acid precursors on muscle and liver metabolism when the dehydrogenase function is impaired.
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Characterization of phenylpyruvic acid (PPA) and beta-benzyl phenylpyruvic acid (BPPA) by UV, IR, MS and 1H NMR has been carried out. It is found that the absorption at 240 and 365 nm are observed in the UV spectrum of PPA and the absorption at 210 nm is the only one in BPPA. These demonstrate that PPA has the olefinic alcohol structure and BPPA hasn't. The IR absorption at 1,624.38 and 1,697.25 cm-1 of PPA are originated from two carboxy C=O because of its gem-diol structure, and the absorption at 1,706.6 and 1,728.6 cm-1 in BPPA is assignable to keto C=O and carboxy C=O, respectively. The main peaks in the MS spectrum of PPA are 164, 119, 91, 65, 45, 39, and BPPA 254, 236, 209, 181, 91, 77, 65, 39. The peaks at 4.124, 6.381, 7.184-7.748, 9.268 are observed in the 1H NMR spectrum of PPA and the peaks in BPPA are 2.90-3.02, 3.29-3.40, 4.73-4.81, 7.04-7.44, 8.99.
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Tracer experiments with 14C-labelled precursors in Iris times hollandica cv. Wedgwood, Reseda Iutea L. And Keseda Odorata L. have demonstrated that 3-(3-carboxyphenyl) alanine and 3-(3-carboxy-4-hydroxyphenyl) alanine can be derived from the corresponding pyruvic acids, presumably by unspecific transaminations, and that (3-carboxyphenyl) glycine and (3-carboxy-4-hydroxyphenyl) glycine can be derived from the corresponding phenylglyoxylic acids. The glycine derivatives are derived from the alanine derivatives, and the corresponding mandelic acids are intermediates in these transformations. The corresponding phenylacetic acids are incorporated only slightly into the glycine derivatives, indicating that oxidation at the benzylic position in the C6-C3 compounds takes place early in the transformation. The corresponding cinamic acids are not metabolized at all in the plants.
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Phenylpyruvic acid is converted at least partially to phenylacetic acid during the normal extraction procedure used to obtain urinary organic acid profiles of phenylketonuric children by gas chromatography. This decarboxylation reaction can be reduced or completely eliminated by forming oxime derivatives prior to extraction.
The oral administration of phenylpyruvic acid to human subjects results in increased urinary excretion of o-hydroxyphenylacetic acid. This demonstrates that phenylpyruvic acid may act as a precursor for o-hydroxy derivatives of phenylalanine and suggests that the formation of o-tyrosine is not necessary to account for the excretion of o-hydroxyphenylacetic acid in phenylketonuria.
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