P-hydroxyphenylacetic acid

Panicum maximum, dried leaves p-Hydroxyphenylacetic acid 74... 

Metabolites of biogeiuc amines have also been analyzed by GC-ECD. For the simultaneous analysis of 5-hydroxyindole-3-acetic acid (5-HIAA), homovanillic acid (HVA) and m- and p-hydroxyphenylacetic acid (m-, p-HPAA), (metabolites of 5-HT, DA, and m- and p-tyramine acid respectively) in urine, a simple acidic extraction followed by derivatization with PFPA (derivatizes phenols) and hexafluoroisopropanol (deriva-tizes carboxylic acid groups) has been used (Davis et al., 1982 Baker et al., 1987). 

Gracin, S. and Rasmuson, A.C. Solubility of phenylacetic acid, p-hydroxyphenylacetic acid, p-aminophenylacetic acid, p-hydroxybenzoic acid, and ibuprofen in pure solvents, / Chem. Eng. Data, 47(6) 1379-1383, 2002. 

The authors report detection limits of 8x10 ° mol/dm for TATP and 8 X lO mol/dm for HMTD. When p-hydroxyphenylacetic acid (p-HPAA) (6) was used as the oxidation substrate instead of ABTS, a highly fluorescent dimer (7) was formed. This dimer could be detected spectrophotometricaUy, although the sensitivity dropped (Eq. (12)). Both methods also enabled a semi-quantitative estimation of TATP and HMTD concentrations [86]. Dimerization of p-hydroxyphenylacetic acid (p-HPAA) by hydrogen peroxide in presence of peroxidase [86] is as foUows ... 

Lumanta IG Jr. 1987. The effects of tyrosine, p-hydroxyphenylacetic acid, p- cresol and bacitracin methylene disalicylate on the growth of weanling pigs. Dissertation Abstracts International 49/04-B 959. 

The fate of monophenolic pressor amines is not so certain. Ewins and Laidlaw found that when large amounts of tyramine were fed to dogs, up to 25% was excreted in the urine as p-hydroxyphenylacetic acid. They found that this occurred when tyramine was perfused through liver and uterus, but when the drug was perfused through the heart it was destroyed (73). Similarly, Bernheim and Bernheim (16) found that the heart was capable of opening the phenolic ring in tyramine. 

P)-hydroxyphenylacetic acid (S)-2,3-dihydroxypropanoic acid (1 S,2S,4P) -trichloro-1,2,4-trim ethylcyclohexane... 

Garcia-Marco, S., Torreblanca, A., and Lucena, J.J. Chromatographic determination of Fe chelated by ethylenediamine-N-(o-hydroxyphenylacetic)-N -(p-hydroxyphenylacetic) acid in commercial EDDHA/Fe fertilizers. J. Agr. Food Chem. 2006, 54, 1380-1386. 

The carbon dioxide is measured manometrically, or the system is coupled to an amine oxidase-peroxidase-p-hydroxyphenylacetic acid system for determining the amine produced (37). Specific decarboxylases are avail-... 

The enzymes are rather nonspecific, so most amines in solution will be determined. The reaction can be monitored by oxygen uptake, aldehyde production, ammonia production, or hydrogen peroxide. By coupling the reaction to peroxidase-p-hydroxyphenylacetic acid the reaction can be followed fiuorimetrically (37). The formation rate of ammonia can be determined conveniently by use of a Beckman 39137 cation selective electrode which permits the determination of 1-100 /xg/ml of amine (19). 

The intermediate formation of 2,5-dihydroxyphenylpyruvic acid in this conversion has not been proved by isolation. But as this is readily metabolized by tyrosine-oxidizing systems (e.g., 489), unlike the possible alternative intermediate p-hydroxyphenylacetic acid, the pathway is not in doubt. On the other hand, the detailed mechanism of this conversion is probably the major unsolved problem in the study of tyrosine metabolism. 

On oxidation, homovanillic acid, HVA (4-hydroxy-3-methoxy-phenyl-acetic acid), is converted to a highly fluorescent, stable compound with an excitation wavelength of 315 nm and an emission wavelength of 425 nm. Oxidized HVA is produced in an amount proportional to that of GOase between 0.001 and 0.25 U/ml (Guil-bault, 1968). Guilbault (1976) showed that p-hydroxyphenylacetic acid has some advantages over HVA with respect to cost and fluorescence coefficient (fluorescence/concentration) and 0.01 U of enzyme could be assayed. 

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