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Biomedical subjects

A Wendel

Publications and source records attributed to A Wendel.

At least 163 records · Page 9Linked to original sources
PubMed1980

In-vivo inhibition by copper and some Cu-complexes of paracetamol-induced lipid peroxidation in benzpyrene-pretreated mice.

Benzo(alpha)pyrene-induced male mice were treated with 200 mg/kg paracetamol. The ethane exhalation of the animals was taken as an in-vivo index of lipid peroxidation: it amounted to 420 98 nmoles of ethane/kg body weight after 4 hours. A dose of 10 mg/kg of bovine superoxide dismutase had no effect on lipid peroxidation. After 4 daily repeated i.p. injections of 5 mg/kg copper-tyrosine or copper-asprinate an inhibition of the ethane exhalation was observed by 97 %. Control experiments indicated that Cu SO4 and tyrosine alone inhibited this drug-induced lipid peroxidation by 21 % and 24 %, respectively. However, the copper-ethylendiamine tetraacetic acid complex was also effective. The experiments show that in vivo various copper compounds effectively depress this type of drug-induced lipid peroxidation at low concentrations.

Acetaminophen↗
PubMed1978

The fate of extracellular glutathione in the rat.

When intravenously administered to rats, [U-14C]glycine-labelled GSSG, GSH and its analogue ophthalmic acid were rapidly removed from the blood. In perfusion studies with isolated liver, however, the compounds did not enter the liver tissue. Thus, uptake by this tissue is obviously not responsible for the removal of gamma-glutamyl tripeptides from the blood. Instead, rapid hydrolysis of the tripeptides was observed. The undegraded tripeptides were only detected in the blood immediately after administration. Within tissue the degradation product glycine accounted for all the radioactivity. After intravenous injection of the labelled tripeptides the radioactivity accumulated first in the kidney, as shown by autoradiographic studies and chemical analysis of different tissues. The hydrolysis of the gamma-glutamyl tripeptides decreased markedly after the renal arteries were clamped. These observations strongly suggest that renal tissue is the principal site of the degradation of the tripeptides. Inhibition studies and experiments with isolated renal tubules revealed that gamma-glutamyl transpeptidase catalyses the fast hydrolysis of the extracellular peptides. The results indicate that, when entering the extracellular space, glutathione and its analogues are completely hydrolysed and must be resynthesized after reuptake of the constituent amino acids. It is concluded that the degradation occurs mainly on the luminal surface of the renal brush-border membrane and that gamma-glutamyl transpeptidase is a glutathionase acting on extracellular glutathione.

Animals↗
PubMed1978

Reactivity of antiinflammatory and superoxide dismutase active Cu(II)-salicylates.

The activity of chelated Cu(II) with four different aspirin-like drugs in various superoxide dismutase assays was examined. Prior to these studies the oxidation state of the involved copper was measured by x-ray photoelectron spectrometry and was found to be +II throughout. All copper complexes were able to suppress the xanthine-xanthine oxidase mediated reduction of both cytochrome c and nitroblue tetrazolium as well as the formazan formation by KO2 in a specific manner. The hydroxylation of benzo-[alpha]-pyrene as well as the demethylation of 7-ethoxycoumarin using induced hepatic rat microsomes could be successfully inhibited by the employed Cu(II) chelates. Cu(II)-acetylsalicylate was the most active copper complex. Our findings support the proposal that Cu(II) chelates are the active forms of aspirin-like antiinflammatory agents.

Animals↗
PubMed1977

Hepatic microsomal dealkylations. Inhibition by a tyrosine-copper (II) complex provided with superoxide dismutase activity.

The effect of a divalent copper-tyrosine complex has been evaluated in rat liver microsome-catalyzed dealkylations. The copper complex, which is provided with superoxide dismutase activity, inhibits at micromolar concentrations aminopyrine, p-nitroanisol, and 7-ethoxycoumarin dealkylations. It has also been found that cumene hydroperoxide-supported p-nitroanisol demethylation, the formation of a 440 nm species, and the formation of superoxide radicals are inhibited by the divalent copper complex. On the other hand, 3-chloroperbenzoic acid has been found to support a copper complex-insensitive 7-ethoxycoumarin dealkylation. Oxygen uptake by rat liver microsomes is also inhibited by the copper complex. The data support the concept that the copper complex acts as a superoxide dismutase at the level of a cytochrome P-450 intermediate species, liganded with superoxide anions.

Aminopyrine N-Demethylase↗
PubMed1976

On the role of gamma-glutamyltransferase in renal tubular amino acid reabsorption.

The degradation of glutathione in the kidney of the rat was investigated in vivo and in vitro. When radioactive glutathione or its analogue ophthalmic acid was administered intravenously to mice or rats, the tripeptides were rapidly and completely degraded. Within the organs, no radioactive glutathione, but only labelled glycine was found. The main part of the degrading activity was localized in the kidney. Kidney homogenate degraded glutathione at a rate of 46.5 nmoles/min per mg of protein. This could be inhibited by the gamma-glutamyltransferase inhibitor serine-borate. Isolated renal tubules degraded the tripeptide at a rate of 18 nmoles/min/mg; this reaction was also inhibited by serine-borate. The whole activity was found in the particulate fraction (100000 xg). Glycine and gamma-glutamylglycine were identified as the radio-active products. The results indicate that gamma-glutamyltransferase is able to split glutathione extracellularly in the lumen of the tubule at a very high rate. It is concluded that the enzyme faces the luminal side of the brush border membrane with respect to its substrate gluthathione. This seems to be incompatible with a basic topological prerequisite for the in vivo function of the gamma-glutamyl cycle in renal tubular amino acid reabsorption.

Animals↗
PubMed1976

[The biosynthesis of glutathione in human erythrocytes (author's transl)].

The concentrations of glutathione precursors in human erythrocytes were investigated. 300muM glutamate, 375 muM glycine, and 10muM cysteine were found by automated amino acid analysis. The concentration of 2-aminobutyrate, the precursor of ophthalmic acid, was 15muM. The influence of the activities of endogenous or added glutamyl-cysteine synthetase and glutathione synthetase on the rate of glutathione biosynthesis was measured in membrane-free hemolysates under physiological conditions. The results show that the rate of the overall biosynthesis mainly depends on the formation of the dipeptide glutamyl-cysteine. The effect of glutathione precursor concentrations on the synthesis of the tripeptide was investigated at constant (endogenous) activities of the synthesizing enzymes. The rate was not enhanced by addition of glutamate and/or glycine unless cysteine or glutamyl-cysteine was also added. It is concluded that the concentration of cysteine limits the actual rate of the glutamyl-cysteine-synthetase reaction in vivo. No cysteine or bis(glutamyl)cystine was detected in human hemolysate; however, these disulfides were converted to glutathione. This indicates that erythrocytes have an appropriate system for their reduction, since the disulfides themselves are not substrates for the glutathione-synthesizing enzymes. Studies with intact human red cells indicate that the uptake of cysteine is the rate-determining step in the biosynthesis of glutathione.

Amino Acids↗
PubMed1976

[Does a modified gamma-glutamyl cycle exist in human erythrocytes (author's transl)].

The first step in the biosynthesis of glutathione is the formation of gamma-glutamyl-cysteine by the enzyme glutamyl-cysteine synthetase. Since this enzyme is not specific for cysteine, different gamma-glutamylamino acids may be formed in vivo which represent potential substrates for the enzymes gamma-glutamylcyclotransferase; in this way 5-oxo-L-proline and free amino acid are formed. We investigated in membrane-free hemolysate the competition between the biosynthesis of glutathione or ophthalmic acid and the degradation of gamma-glutamyl peptides by measuring the formation of 5-oxoproline. The endogenous rate of 5-oxoproline production was 0.13 muM/min. This increased to 2muM/min after addition of 2-aminobutyrate, and to 10muM/min after addition of glutamate and 2-aminobutyrate to hemolysate. Addition of cysteine resulted in an increased oxoproline production only under conditions where glutamyl-cysteine accumulated. In addition, it was shown that for glutamyl-2-aminobutyrate the degradation to 5-oxoproline is faster than the utilization for the tripeptide synthesis. This was not the case for glutamyl-cysteine. Since membrane-free hemolysate (which lacks gamma-glutamyltransferase) is able to produce 5-oxoproline starting from glutamate, it is concluded that this 5-oxoprolinent amino acid transport via a modified gamma-glutamyl cycle.

Aminobutyrates↗
PubMed1976

Molecular and kinetic properties of 15-hydroxyprostaglandin dehydrogenase (PG-15-HDH) from human placenta.

Some molecular properties of PG-15-HDH from human term placenta were investigated. Using a computer-based weighted linear regression analysis, intersecting initial rate patterns were received for the forward reaction with the prostaglandins (PG) E1, E2, and F2alpha, respectively, and NAD as substrates. NADH exerted a linear competitive inhibition with respect to NAD. The 15-ketoprostaglandins (15-keto-PG) E1 and F2alpha showed a linear noncompetitive inhibition with respect to their corresponding PG. The kinetic patterns suggest an ordered Bi Bi mechanism of PG-15-HDH reaction. The results are discussed with respect to their possible biological significance.

Alcohol Oxidoreductases↗
PubMed1975

Substrate-induced redox change of selenium in glutathione peroxidase studied by x-ray photoelectron spectroscopy.

Glutathione peroxidase showed an X-ray photoelectron spectroscopy signal of the Se 3d (3/2, 5/2) electrons at 54.4 eV. After the addition of the acceptor substrate H2O2, a marked shift of this signal to a value of 58.0 eV was observed. Upon subsequent treatment with the donor substrate glutathione, this chemical shift was reversed and the original signal was obtained. These data demonstrate that the enzyme-bound selenium moiety participates in the catalytic process. From the chemical shift obtained it is concluded that the enzyme shuttles between a selenol or selenol derivative in its reduced form and a seleninyl or selenonyl compound in its oxidized form.

Deuterium↗
PubMed1975

5-Oxoprolinase from rat kidney, I. Assay, purification, and determination of kinetic parameters.

A new assay for the determination of 5-oxoprolinase activity is described. The enzyme 5-oxoprolinase was purified from rat kidney 285-fold to apparent homogeneity, as judged by analytical disc electrophoresis and discontinous polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate. The specific activity of the preparation was 122 mU/mg of protein. A complete initial rate kinetic analysis of the forward reaction catalyzed by 5-oxoprolinase was carried out using 5-oxo-L-proline and MgATP2theta as substrates. The computer-fitted double reciprocal plots showed intersecting patterns indicating a sequential mechanism. The data were fitted by weighted linear regression analysis using the complete equation for bisubstrate reactions. The limiting Michaelis constants for 5-oxoproline and MgATP2theta were calculated to be 31.6 +/- 2.3 muM and 172.7 +/- 11.5muM, respectively. The maximum forward rate is 1.2 +/- 0.02 mumol X min-1; the turnover number 7.0 min-1.

Adenosine Triphosphate↗
PubMed1975

5-Oxoprolinase from rat kidney, II. Molecular weight determinations.

The molecular weight of 5-oxoprolinase from rat kidney was estimated by gel filtration on Sephadex G-200 and G-150 to be 460 000 +/- 30 000. A value of 230 000 +/- 10 000 was obtained by zonal sedimentation in a sucrose gradient. Polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate yielded a molecular weightof 115 000 +/- 6 000. It is concluded that 5-oxoprolinase consists of four subunits of 115 000 daltons each. The dissociation or aggregation behavior of the enzyme seems to be influenced neither by the presence of the substrates 5-oxo-L-proline and MgATP2theta nor by the presence of the stabilizing compounds glutathione mercaptoethanol or dithioerythritol.

Amidohydrolases↗