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PubMed1986

Tyrosinase catalyzes an unusual oxidative decarboxylation of 3,4-dihydroxymandelate.

Tyrosinase usually catalyzes the conversion of monophenols to o-diphenols and oxidation of diphenols to the corresponding quinones. However, when 3,4-dihydroxymandelic acid was provided as the substrate, it catalyzed an unusual oxidative decarboxylation reaction generating 3,4-dihydroxybenzaldehyde as the sole product. The identity of the product was confirmed by high-performance liquid chromatography (HPLC) as well as ultraviolet and infrared spectral studies. None of the following enzymes tested catalyzed the new reaction: galactose oxidase, ceruloplasmin, superoxide dismutase, ascorbate oxidase, dopamine beta-hydroxylase, and peroxidase. Phenol oxidase inhibitors such as phenylthiourea, potassium cyanide, and sodium azide inhibited the reaction drastically, suggesting the participation of the active site copper of the enzyme in the catalysis. Mimosine, a well-known competitive inhibitor of tyrosinase, competitively inhibited the new reaction also. 4-Hydroxymandelic acid and 3-methoxy-4-hydroxymandelic acid neither served as substrates nor inhibited the reaction. Putative intermediates such as 3,4-dihydroxybenzyl alcohol and (3,4-dihydroxybenzoyl)formic acid did not accumulate during the reaction. Oxidation to a quinone methide derivative rather than conventional quinone accounts for this unusual oxidative decarboxylation reaction. Earlier from this laboratory, we reported the conversion of 4-alkylcatechols to quinone methides catalyzed by a cuticular phenol oxidase [Sugumaran, M., & Lipke, H. (1983) FEBS Lett. 155, 65-68]. Present studies demonstrate that mushroom tyrosinase will also catalyze quinone methide production with the same active site copper if a suitable substrate such as 3,4-dihydroxymandelic acid is provided.

Basidiomycota↗
PubMed2004

Heptakis(6-amino-6-deoxy)-beta-cyclodextrin as a chiral selector for the separation of anionic analyte enantiomers by capillary electrophoresis.

A hepta-substituted beta-cyclodextrin bearing seven amino groups, heptakis(6-amino-6-deoxy)-beta-cyclodextrin (per-6-NH2-beta-CD) was successfully used as a chiral selector for the enantioseparation of different anionic analytes. The running buffer pH and chiral selector concentration were the studied parameters crucial in achieving the maximum possible enantioresolution. Enantiomeric separation of a mixture of seven carboxybenzyl-amino acids was achieved in 24 min. Excellent resolution was obtained for carboxybenzyl-tryptophan (Rs = 11.2).

Amino Acids↗
PubMed1983

The metabolism of L-m-tyrosine: the use of a putative precursor to investigate the increased production of m-hydroxymandelic acid in phenylketonuria.

Several urinary meta-substituted phenols appear to be of endogenous origin. However, the production of these compounds is reduced in phenylketonuria with the exception of m-hydroxymandelic acid whose excretion is approximately doubled. This phenomenon has been investigated in two patients with phenylketonuria using the putative precursor L-m-tyrosine labelled with deuterium. Metabolism of this compound in these patients was comparable to that in healthy adults although much less was converted to m-hydroxymandelic acid and the excretion pattern of this metabolite was different. This apparent anomaly is attributed to smaller metabolic compartments in phenylketonuria and a lower threshold for the metabolism of m-tyramine via beta-hydroxylation. Incorporation into the natural pathway was shown by depletion of endogenous m-hydroxymandelic acid. The results are further support for the ideas that the amine precursors of m-hydroxymandelic acid, m-tyramine and m-octopamine, have a functional role and may be important in the pathogenesis of phenylketonuria.

2-Hydroxyphenethylamine↗
PubMed2005

Making thiamin work faster: acid-promoted separation of carbon dioxide.

The conjugate of thiamin and benzoylformate, mandelylthiamin (MTh), undergoes decarboxylation about 106 times slower than the analogous enzymic intermediate. It has now been discovered that the decarboxylation of MTh is accelerated by the acid component of pyridine and 4-picoline buffers. There is no role for a proton donor to stabilize the transition state for decarboxylation: catalysis must be achieved by the acid's trapping the product carbanion, preventing recarboxylation. This requires that diffusion of CO2 is rate-determining, and that protonation of the carbanion allows this to occur. This interpretation correctly predicts that the same acid components will prevent a fragmentation reaction by protonating the intermediate, which fragments only as the conjugate base.

Acids↗
PubMed1981

Promotion of carbohydrate oxidation in the heart by some phenylglyoxylic acids.

A series of phenylglyoxylic acids is described, many of which are able to promote carbohydrate oxidation in muscle tissue, thereby favorably altering the carbohydrate/fatty acid balance in situations where fatty acid utilization is elevated. Such situations are reported to occur in ischemic heart disease, particularly following myocardial infection. In an attempt to effectively deliver the phenylglyoxylic acids to the site of action within the cell, the L-(+)-phenylglycines were employed as prodrugs. These are known to be transaminated to phenylglyoxylic acids. L-(+)-2-(4-Hydroxyphenyl)glycine (25, oxfenicine) has been selected for clinical evaluation.

Amino Acids↗
PubMed1988

Analysis of the in vitro pharmacologic response of renal pelvis and detrusor smooth muscle to thiphenamil, oxybutynin and verapamil.

A new computerized methodology was used to acquire and analyze the relative pharmacologic sensitivity of the renal pelvis and urinary bladder of the rabbit to pharmacologic stimulation. Comparison was made of the effects of thiphenamil, verapamil and oxybutynin on the spontaneous contractions of isolated detrusor and renal pelvis. Data collected by computer were evaluated in terms of amplitude, frequency, and tension change to varying concentration of pharmacologic stimulation. Data were analyzed using a frequency/time domain algorithm developed specifically to evaluate the contribution of the oscillatory components of tension associated with smooth muscle tissues. For the renal pelvis the results show 6 X 10(-5) M thiphenamil, 10(-3) M oxybutynin, and 5 X 10(-6) M verapamil resulted in a 50% inhibition of the phasic contractions. Thiphenamil significantly increased the contractile frequency of the renal pelvis. For the bladder 10(-3) M thiphenamil resulted in a 50% inhibition of the phasic contractions, while 3 X 10(-4) M oxybutynin and 3 X 10(-6) M verapamil were needed to achieve the same level of inhibition. Thiphenamil at lower doses (10(-4) M to 5 X 10(-4) M) showed a biphasic effect--an increase of the bladder tissue activity followed by a relaxation phase--that oxybutynin and verapamil failed to produce. The results show that the calcium blocker suppresses the spontaneous activity of the upper and lower urinary tract at lower concentrations than the anticholinergic or thiphenamil.

Animals↗
PubMed1978

[Gas chromatographic estimation of acidic urinary metabolites after separation on prepacked silica gel columns (author's transl)].

The acidic ethylacetate extracts of 24-h urine specimens are evaporated and redissolved in chloroform--methanol--acetic acid. The resulting solution is transferred to a prepacked silica gel column. Elution takes 160 min using a specially designed chloroform--methanol--acetic acid gradient. The eluate is divided into fractions (16 min each) which are evaporated to dryness. The residues are silvlated and determined quantitatively by gas chromatography. The capacity of the silica gel column allows analysis of 30% of a 24-h urine specimen. In consequence, metabolites can be quantitated at concentrations less than 1 mg per 24 h. The method is suitable to obtain more detailed metabolic profiles of the carboxylic acids in urine.

Benzoates↗
PubMed1982

Human exposure to styrene. IV. Industrial hygiene investigations and biological monitoring in the polyester industry.

An industrial hygiene study of 10 glassfiber reinforced polyester plants (including 90 workers) was undertaken to investigate the styrene exposure in this industry and to estimate biological limit values (BLV's) for the urinary metabolites of styrene: mandelic (MA) and phenylglyoxylic acids (PGA). Time weighted average (TWA) styrene exposures were found ranging from 2 to 200 ppm. The urinary elimination of metabolites correlated well with exposure and the BLV's corresponding to an 8-h exposure at 100 ppm were consistent with earlier laboratory findings (end-of-shift sample: MA 1640, PGA 510, MA + PGA 2150; next-morning sample: MA 330, PGA 330, MA + PGA 660 mg/g creat.). Total metabolites (MA + PGA) in the next-morning sample or mandelic acid in the end-of-shift sample are recommended for routine monitoring of exposure to styrene. The study revealed the need for further research on how to reduce styrene exposure in this industry.

Air↗