Metabolism of normetanephrine-H3 in rat brain--identification of conjugated 3-methoxy-4-hydrophenylglycol as the major metabolite

Normetanephrine-H3 injected into the cisterna magna of rats is rapidly metabolized and disappears from brain with an initial half-life of about 12 min. Monoamine oxidase inhibition prevents almost completely the conversion of normetanephrine-H3 to other metabolites and markedly diminishes the rate of disappearance of radioactivity from brain ( T 1 2 = 2 · 4 hr ). These data show that normetanephrine is normally metabolized primarily by monoamine oxidase and that unaltered normetanephrine does not readily pass out of the brain. Free 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3-methoxy-4-hydroxymandelic acid (VMA) formed from intracistemally injected normetanephrine-H3 represent only a small fraction of the radioactivity in brain. The major metabolite was identified as the sulfate conjugate of MHPG. After intracisternal administration of norepinephrine-H3, 3-methoxy-4-hydroxyphenylgIycol sulfate (MHPG-SO4) was also found to be the major metabolite present in brain. These findings suggest that deamination, reduction, and subsequent corrugation with sulfate is the primary route of metabolism of normetanephrine in rat brain and that norepinephrine is also metabolized to this sulfate conjugate.

Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. I. Synthesis of enzymes by the wild type

Hegeman, G. D. (University of California, Berkeley). Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. I. Synthesis of enzymes by the wild type. J. Bacteriol. 91:1140-1154. 1966.-The control of synthesis of the five enzymes responsible for the conversion of d(-)-mandelate to benzoate by Pseudomonas putida was investigated. The first three compounds occurring in the pathway, d(-)-mandelate, l(+)-mandelate, and benzoylformate, are equipotent inducers of all five enzymes. A nonmetabolizable inducer, phenoxyacetate, also induces synthesis of these enzymes; but, unlike the metabolizable inducer-substrates, it does not elicit synthesis of enzymes that mediate steps in the pathway beyond benzoate. Under conditions of semigratuity, dl-mandelate elicits immediate synthesis at a steady rate of the first two enzymes of the pathway, but two enzymes which act below the level of benzoate are synthesized only after a considerable lag. Succinate and asparagine do not significantly repress the synthesis of the enzymes responsible for mandelate oxidation.

Brain concentrations of biogenic amine metabolites in acutely treated and ethanol-dependent rats

1 Mass fragmentography was used to measure whole brain concentrations of some of the major metabolites of tyramine, octopamine, dopamine and noradrenaline in acutely treated and in ethanol-dependent rats. 2 Treatments with ethanol, either acutely or chronically, failed to alter significantly brain concentration of p-hydroxphenylacetic and p-hydroxymandelic acid (metabolites derived from tyramine and octopamine respectively). The effect on catecholamine metabolites was marked and therefore suggests that ethanol is selective in its effect on central metabolism of biogenic amines. 3 Acute ethanol treatment significantly increased brain concentration of homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxy-4-hydroxyphenylglycol (MHPG). Vanilmandelic acid (VMA) was not affected. All four metabolites (HVA, DOPAC, MHPG and VMA) were increased in the brains of rats rendered dependent on ethanol while still intoxicated (blood ethanol levels above 200 mg/dl). In ethanol-dependent rats undergoing ethanol withdrawal syndrome (no ethanol present in blood), the brain concentrations of HVA and DOPAC were normal while those of MHPG and VMA continued to be elevated. 4 From the decline in the concentrations of HVA and DOPAC after 50 mg pargyline/kg in control rats and rats acutely treated with ethanol, it was concluded that ethanol has no effect on the transport of phenolic acids across the blood brain barrier. 5 No reversal in the metabolism of catecholamines from an oxidative to a reductive pathway, analogous to that produced by ethanol in the periphery, could be established in the brain. 6 The increase in catecholamine metabolite concentrations after ethanol treatment, either acute or chronic, were interpreted as manifestations of increases catecholamine turnover.

Mandelate pathway of Pseudomonas putida: sequence relationships involving mandelate racemase, (S)-mandelate dehydrogenase, and benzoylformate decarboxylase and expression of benzoylformate decarboxylase in Escherichia coli

The genes that encode the five known enzymes of the mandelate pathway of Pseudomonas putida (ATCC 12633), mandelate racemase (mdlA), (S)-mandelate dehydrogenase (mdlB), benzoylformate decarboxylase (mdlC), NAD(+)-dependent benzaldehyde dehydrogenase (mdlD), and NADP(+)-dependent benzaldehyde dehydrogenase (mdlE), have been cloned. The genes for (S)-mandelate dehydrogenase and benzoylformate decarboxylase have been sequenced; these genes and that for mandelate racemase [Ransom, S. C., Gerlt, J. A., Powers, V. M., & Kenyon, G. L. (1988) Biochemistry 27, 540] are organized in an operon (mdlCBA). Mandelate racemase has regions of sequence similarity to muconate lactonizing enzymes I and II from P. putida. (S)-Mandelate dehydrogenase is predicted to be 393 amino acids in length and to have a molecular weight of 43,352; it has regions of sequence similarity to glycolate oxidase from spinach and ferricytochrome b2 lactate dehydrogenase from yeast. Benzoylformate decarboxylase is predicted to be 499 amino acids in length and to have a molecular weight of 53,621; it has regions of sequence similarity to enzymes that decarboxylate pyruvate with thiamin pyrophosphate as cofactor. These observations support the hypothesis that the mandelate pathway evolved by recruitment of enzymes from preexisting metabolic pathways. The gene for benzoylformate decarboxylase has been expressed in Escherichia coli with the trc promoter, and homogeneous enzyme has been isolated from induced cells.

Production of R-(-)-mandelic acid from mandelonitrile by Alcaligenes faecalis ATCC 8750

R-(-)-Mandelic acid was produced from racemic mandelonitrile by Alcaligenes faecalis ATCC 8750. Ammonium acetate or L-glutamic acid as the carbon source and n-butyronitrile as the inducer in the culture medium were effective for bacterial growth and the induction of R-(-)-mandelic acid-producing activity. The R-(-)-mandelic acid formed from mandelonitrile by resting cells was present in a 100% enantiomeric excess. A. faecalis ATCC 8750 has an R-enantioselective nitrilase for mandelonitrile and an amidase for mandelamide. As R-(-)-mandelic acid was produced from racemic mandelonitrile in a yield of 91%, whereas no S-mandelonitrile was left, the S-mandelonitrile remaining in the reaction is spontaneously racemized because of the chemical equilibrium and is used as the substrate. Consequently, almost all the mandelonitrile is consumed and converted to R-(-)-mandelic acid. R-(-)-Mandelic acid was also produced when benzaldehyde plus HCN was used as the substrate.

Catecholamines in plasma and urine at high altitude

The concentration of free epinephrine and norepinephrine in plasma and 24-hr urine samples, collected from members of the Dutch Monte Rosa expedition (July 1963) was investigated during 17 days at various altitudes up to 4,560 m. The results indicate that the levels of both plasma and urine catecholamines were elevated during the expedition, the plasma levels reaching a maximum towards the end of the 12 days sojourn at 4,560 m. In general there was a twofold increase in total catecholamine concentration in the samples collected at high altitude as compared to control values at sea level. This difference was due to a significant increase in the norepinephrine concentration; there was little change in epinephrine level.

epinephrine and norepinephrine; sympathoadrenal activity

Submitted on September 2, 1964

On the origin of enzymatic species

The diversity of enzyme catalytic function is remarkable, particularly when one considers that ancestral life forms must have started with a much smaller ensemble of proteins. In this article, we discuss the evolution of the mandelate pathway in pseudomonads as an example of how catalytic diversity may have evolved. We suggest that existing enzymes that catalyse the chemistry needed to accomplish a transformation were recruited, followed by the evolution of specific binding.

Mechanism of the reaction catalyzed by mandelate racemase. 2. Crystal structure of mandelate racemase at 2.5-A resolution: identification of the active site and possible catalytic residues

The crystal structure of mandelate racemase (MR) has been solved at 3.0-A resolution by multiple isomorphous replacement and subsequently refined against X-ray diffraction data to 2.5-A resolution by use of both molecular dynamics refinement (XPLOR) and restrained least-squares refinement (PROLSQ). The current crystallographic R-factor for this structure is 18.3%. MR is composed of two major structural domains and a third, smaller, C-terminal domain. The N-terminal domain has an alpha + beta topology consisting of a three-stranded antiparallel beta-sheet followed by an antiparallel four alpha-helix bundle. The central domain is a singly wound parallel alpha/beta-barrel composed of eight central strands of beta-sheet and seven alpha-helices. The C-terminal domain consists of an irregular L-shaped loop with several short sections of antiparallel beta-sheet and two short alpha-helices. This C-terminal domain partially covers the junction between the major domains and occupies a region of the central domain that is filled by an eight alpha-helix in all other known parallel alpha/beta-barrels except for the barrel domain in muconate lactonizing enzyme (MLE) [Goldman, A., Ollis, D. L., & Steitz, T. A. (1987) J. Mol. Biol. 194, 143] whose overall polypeptide fold and amino acid sequence are strikingly similar to those of MR [Neidhart, D. J., Kenyon, G. L., Gerlt, J. A., & Petsko, G. A. (1990) Nature 347, 692]. In addition, the crystal structure reveals that, like MLE, MR is tightly packed as an octamer of identical subunits. The active site of MR is located between the two major domains, at the C-terminal ends of the beta-strands in the alpha/beta-barrel domain. The catalytically essential divalent metal ion is ligated by three side-chain carboxyl groups contributed by residues of the central beta-sheet. A model of a productive substrate complex of MR has been constructed on the basis of difference Fourier analysis at 3.5-A resolution of a complex between MR and (R,S)-p-iodomandelate, permitting identification of residues that may participate in substrate binding and catalysis. The ionizable groups of both Lys 166 and His 297 are positioned to interact with the chiral center of substrate, suggesting that both of these residues may function as acid/base catalysts.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzymes of the mandelate pathway in Bacterium N.C.I.B. 8250

1. Bacterium N.C.I.B. 8250 was grown on dl-mandelate, benzyl alcohol, benzoyl-formate, benzaldehyde and benzoate and also on 2-hydroxy, 4-hydroxy, 3,4-dihydroxy and 4-hydroxy-3-methoxy analogues of these compounds. The enzymic complements of the cells were determined and the specificities of some of the enzymes examined. 2. Growth on mandelate or benzoylformate induces l-mandelate dehydrogenase, benzoylformate decarboxylase, benzyl alcohol dehydrogenase and a heat-stable as well as a heat-labile benzaldehyde dehydrogenase. Growth on benzyl alcohol or benzaldehyde induces benzyl alcohol dehydrogenase and the heat-labile benzaldehyde dehydrogenase. 3. The enzymes of the mandelate-to-benzoate pathway are non-specifically active on, and induced by, all the substituted analogues that support growth. 4. Benzoate oxidase is induced by growth on benzoate or on 2-hydroxybenzoate. 2-Hydroxybenzoate hydroxylase, 4-hydroxybenzoate hydroxylase and 4-hydroxy-3-methoxybenzoate O-demethylase are induced only by growth on homologous substrates. 5. The results of the investigation are discussed with regard to the possible regulation of the enzyme systems.

Thiomandelic acid, a broad spectrum inhibitor of zinc beta-lactamases: kinetic and spectroscopic studies

Resistance to beta-lactam antibiotics mediated by metallo-beta-lactamases is an increasingly worrying clinical problem. Candidate inhibitors include mercaptocarboxylic acids, and we report studies of a simple such compound, thiomandelic acid. A series of 35 analogues were synthesized and examined as metallo-beta-lactamase inhibitors. The K(i) values (Bacillus cereus enzyme) are 0.09 microm for R-thiomandelic acid and 1.28 microm for the S-isomer. Structure-activity relationships show that the thiol is essential for activity and the carboxylate increases potency; the affinity is greatest when these groups are close together. Thioesters of thiomandelic acid are substrates for the enzyme, liberating thiomandelic acid, suggesting a starting point for the design of "pro-drugs." Importantly, thiomandelic acid is a broad spectrum inhibitor of metallo-beta-lactamases, with a submicromolar K(i) value for all nine enzymes tested, except the Aeromonas hydrophila enzyme; such a wide spectrum of activity is unprecedented. The binding of thiomandelic acid to the B. cereus enzyme was studied by NMR; the results are consistent with the idea that the inhibitor thiol binds to both zinc ions, while its carboxylate binds to Arg(91). Amide chemical shift perturbations for residues 30-40 (the beta(3)-beta(4) loop) suggest that this small inhibitor induces a movement of this loop of the kind seen for other larger inhibitors.

Oxidation of monomethoxylated aromatic compounds by lignin peroxidase: role of veratryl alcohol in lignin biodegradation

Lignin peroxidase (LiP), an extracellular heme enzyme from the lignin-degrading fungus Phanerochaete chrysosporium, catalyzes the H2O2-dependent oxidation of a variety of nonphenolic lignin model compounds. The oxidation of monomethoxylated lignin model compounds, such as anisyl alcohol (AA), and the role of veratryl alcohol (VA) in LiP reactions were studied. AA oxidation reached a maximum at relatively low H2O2 concentrations, beyond which the extent of the reactions decreased. The presence of VA did not affect AA oxidation at low molar ratios of H2O2 to enzyme; however, at ratios above 100, the presence of VA abolished the decrease in AA oxidation. Addition of stoichiometric amounts of AA to LiP compound II (LiPII) resulted in its reduction to the native enzyme at rates that were significantly faster than the spontaneous rate of reduction, indicating that AA and other monomethoxylated aromatics are directly oxidized by LiP, albeit slowly. Under steady-state conditions in the presence of excess H2O2 and VA, a visible spectrum for LiPII was obtained. In contrast, under steady-state conditions in the presence of AA a visible spectrum was obtained for LiPIII*, a noncovalent complex of LiPIII and H2O2. AA competitively inhibited the oxidation of VA by LiP; the Ki for AA inhibition was 32 microM. Addition of VA to LiPIII* resulted in its conversion to the native enzyme. In contrast, AA did not convert LiPIII* to the native enzyme; instead, LiPIII* was bleached in the presence of AA. Thus, AA does not protect LiP from inactivation by H2O2.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Lifetime and reactivity of the veratryl alcohol radical cation. Implications for lignin peroxidase catalysis

The formation and decay of veratryl alcohol radical cation upon oxidation of veratryl alcohol by thallium (II) ions was studied by pulse radiolysis with spectrophotometric and conductometric detection. In aqueous solution at pH 3 the radical cation decays by a first order process, assigned to the deprotonation from the alpha-carbon. On the basis of its lifetime (59 +/- 8 ms) and of its ability to oxidize a polymeric dye (Poly R-478) we estimate that the radical cation can diffuse about 7 microns in an aqueous environment to act as a mediator of oxidations over long distances. However, 4-methoxymandelic acid is not oxidized by the veratryl alcohol radical cation in homogeneous solution, and the comparison with previous studies on lignin peroxidase catalysis suggests a second role for veratryl alcohol radical cation in the enzyme action: it may exist as an enzyme-bound species that has either a longer lifetime or a higher reduction potential than the free radical cation in bulk solution.

Pharmacokinetics and metabolism of transdermal oxybutynin: in vitro and in vivo performance of a novel delivery system

PURPOSE

The purpose of this work was to characterize in vitro/in vivo delivery and pharmacokinetics of oxybutynin (OXY) and its active metabolite. N-desethyloxybutynin (DEO), by a novel matrix transdermal system (TDS).

METHODS

Two in vivo, randomized, three-way crossover trials examined single/multiple OXY TDS doses. Abdomen, buttock, and hip application sites were compared and dose proportionality was evaluated. Model independent pharmacokinetics, elimination rate constants, and metabolite/drug ratios were derived from both plasma OXY and DEO concentrations.

RESULTS

Single/multiple applications of the OXY TDS to the abdomen yielded mean Cmax OXY concentrations of 3.4 +/- 1.1/6.6 +/- 2.4 ng/mL and median tmax of 36/10 h, with steady state achieved during the second application. Plasma OXY and DEO concentrations decreased gradually after Cmax until system removal. Buttock and hip applications resulted in bioequivalent OXY absorption. AUC ratios of DEO/OXY were 1.5 +/- 0.4 (single dose) and 1.3 +/- 0.3 (multiple dose). Mean in vitro OXY skin absorption (186 microg/h) was comparable to the estimated in vivo delivery (163 microg/h) over 96 h.

CONCLUSIONS

Sustained delivery over 4 days and multiple sites allow a convenient, well-tolerated, twice-weekly OXY TDS dosing. A low incidence of anticholinergic side effects is expected during clinical use because of the avoidance of presystemic metabolism and low DEO plasma concentrations. The consistent delivery, absorption, and pharmacokinetics should result in an effective treatment of patients with overactive bladder.

Cefamandole: in vitro and clinical pharmacokinetics

Cefamandole has a broader spectrum and greater potency than the other cephalosporins. It includes Haemophilus influenzae, most strains of Enterobacter, and many strains of indole-positive Proteus and Bacteroides, with a lower minimal inhibitory concentration for Escherichia coli, Klebsiella, etc. Concentrations of drug in the serum after the parenteral injection of cefamandole exceed manyfold the minimal inhibitory concentrations of over 82% of the bacteria studied. Approximately 65 to 85% is excreted in a biologically active form in the urine. This antibiotic offers advantages of antibacterial effectiveness and at the same time retains the safety of penicillin G and cephalothin in animals.

Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. 3. Isolation and properties of constitutive mutants

Hegeman, G. D. (University of California, Berkeley). Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. III. Isolation and properties of constitutive mutants. J. Bacteriol. 91:1161-1167. 1966.-Mutants of Pseudomonas putida constitutive for the synthesis of l(+)-mandelate dehydrogenase were obtained after mandelate- or benzoylformate-limited growth in a chemostat. When grown in media noninducing for the wild type, the mutants are capable of coordinate, constitutive synthesis of the first five enzymes of the mandelate pathway. Later enzymes of the pathway that were examined are normally repressed. The constitutive mutants have two other noteworthy properties: they are superinducible by some compounds which induce the mandelate group enzymes in the wild type, or as a result of exhaustion of the carbon and energy source of the medium in which they are grown; and they exhibit a decreased specificity of induction, being inducible by a wide range of compounds devoid of inductive function for the wild type. These results, together with other evidence indicating that the five mandelate group enzymes comprise a regulatory unit, are discussed and evaluated in the context of the general problem of the regulation of complex dissimilatory pathways.

Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. II. Isolation and properties of blocked mutants

Hegeman, G. D. (University of California, Berkeley). Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. II. Isolation and properties of blocked mutants. J. Bacteriol. 91:1155-1160. 1966.-Mutants of Pseudomonas putida blocked in early reactions of the pathway for oxidation of d-mandelate were isolated and partially characterized. The specific genetic lesions in these mutants made normal inducer-metabolites of the pathway nonmetabolizable. Under the conditions of gratuitous enzyme synthesis so obtained, it could be shown that the d and l isomers of mandelate are equipotent inducers, and that the synthesis of the first five enzymes of the mandelate pathway is coordinate. Further experiments with the blocked mutants showed that benzoylformate, the third intermediate of the pathway, acts as an inducer without prior conversion to mandelate, and that there is no inducible, concentrating permease for mandelate.

Mechanism of the reaction catalyzed by mandelate racemase: importance of electrophilic catalysis by glutamic acid 317

In the high-resolution X-ray structure of mandelate racemase (MR) with the competitive inhibitor (S)-atrolactate bound in the active site [Landro, J. A., Gerlt, J. A., Kozarich, J. W., Koo, C. W., Shah, V. J., Kenyon, G. L., Neidhart, D. J., Fujita, J., & Petsko, G. A. (1994) Biochemistry 33, 635-643], the carboxylic acid group of Glu 317 is hydrogen-bonded to the carboxylate group of the bound inhibitor. This geometry suggests that the carboxylic acid functional group of Glu 317 participates as a general acid catalyst in the concerted general acid-general base catalyzed formation of a stabilized enolic tautomer of mandelic acid as a reaction intermediate. To test this hypothesis, the E317Q mutant of MR was constructed and subjected to high-resolution X-ray structural analysis in the presence of (S)-atrolactate. No conformational alterations were observed to accompany the E317Q substitution at 2.1 A resolution. The values for kcat were reduced 4.5 x 10(3)-fold for (R)-mandelate and 2.9 x 10(4)-fold for (S)-mandelate; the values for kcat/Km were reduced 3 x 10(4)-fold. The substrate and solvent deuterium isotope effects measured for both wild-type MR and the E317Q mutant are not multiplicative when deuteriated substrate is studied in D2O, which suggests that the reactions catalyzed by both enzymes are stepwise and involve the formation of stabilized enolic intermediates. In contrast to wild-type MR, E317Q does not catalyze detectable elimination of bromide ion from either enantiomer of p-(bromomethyl)mandelate. However, E317Q is irreversibly inactivated by racemic alpha-phenylglycidate at a rate comparable to that measured for wild-type MR. Taken together, these mechanistic properties confirm the importance of Glu 317 as a general acid catalyst in the reaction catalyzed by wild-type MR. The kcat for wild-type MR and the reduction in kcat observed for E317O are discussed in terms of the analysis recently described by Gerlt and Gassman for understanding the rates and mechanisms of enzyme-catalyzed proton abstraction reactions from carbon acids [Gerlt, J. A., & Gassman, P. G. (1993) J. Am. Chem. Soc. 115, 11552-11568; Gerlt, J. A., & Gassman, P. G. (1993) Biochemistry 32, 11943-11952].