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PubMed1994

Semiempirical calculations of the oxygen equilibrium isotope effect on binding of oxamate to lactate dehydrogenase.

Semiempirical methods have been used in an attempt to predict theoretically the experimentally observed value of 0.9840 for the oxygen isotope effect on binding of oxamate to lactate dehydrogenase. The overall strategy involved vibrational analysis of oxamate in two different environments; that of the active site residues and in aqueous solution. The comparison of calculated values with the experimentally determined isotope effect proved the AM1 Hamiltonian to be superior to the PM3 Hamiltonian in this modelling. While most tested methods of accounting for solvent effects on the vibrational frequencies of the solute yielded similar results it turned out that what was crucial for the purpose of determination of the isotope effect was the model of oxamate in the active site of the enzyme. In particular, the major factor responsible for the inverse value of this isotope effect can be ascribed to the formation of an ordered, bifurcated hydrogen bond between the oxamate carboxylate and the guanidinium group of the active site histidine.

Animals↗
PubMed1975

Purification and properties of a fructose-1,6-diphosphate activated L-lactate dehydrogenase from Staphylococcus epidermidis.

L-(+)-lactate dehydrogenase (LDH) from Staphylococcus epidermidis ATCC 14990 was purified by affinity chromatography. The purified enzyme was specifically activated by fructose-1,6-diphosphate (FDP). The concentration of FDP required for 50% maximal activity was about 0.15 mM. The enzyme activity was inhibited by adenosine diphosphate (ADP) and oxamate. The inhibition by ADP appeared to be competitive with respect to reduced nicotinamide adenine dinucleotide (NADH). The catalytic activity of the LDH for pyruvate reduction exhibited an optimum at pH 5.6. The enzyme is composed of four, probably identical, subunits. Sephadex gel filtration and sedimentation velocity at pH 5.6 Yielded molecular weights of about 130 000 and 126 000, respectively. The molecular weight at pH 6.5 and 7.0 was found to be only about 68 000. Polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate and sedimentation velocity at pH 2.0 or 8.5 revealed monomeric subunits with an approximate molecular weight of 36000. The thermostability of the heat labile enzyme was increased in the presence of FDP, NADH and pyruvate. The purified LDH exhibited an anomalous type of kinetic behavior. Plots of initial velocity vs. different concentrations of pyruvate, NADH or FDP led to saturation curves with intermediary plateau regions. As a consequence of these plateau regions the Hill coefficient alternated between lower and higher n-values. Some distinguishing properties of the S. epidermidis LDH and other LDHs activated by FDP are discussed.

Adenine Nucleotides↗
PubMed1977

Structural identification of p-dioxane-2-one as the major urinary metabolite of p-dioxane.

Analysis by gas chromatography (GC) of the volatile compounds present in the urine from rats administered dioxane, a hepatic carcinogen to this species, revealed a major metabolite. The appearance of the metabolite was pH-dependent, undetectable at high pH; reacidification of the urine sample brought about the reappearance of the metabolite. The amount excreted was dose-dependent and time-dependent, reaching a maximum between 20 and 28 h after dioxane administration. Diethylene glycol administered to rats gave rise to the same metabolite. When isolated and purified from lyophilized urine by preparative GC, the metabolite exhibited an intense carbonyl band at 1750 cm-1 in the infrared spectrum. Nuclear magnetic resonance spectrum showed two triplets and one singlet with equal intensity at delta 3.85, 4.48 and 4.37, respectively. GC-mass spectrometric studies indicated a parent peak at m/e 102. The metabolite was identified as p-dioxane-2-one. Synthetic reference compound exhibited identical IR, NMR, and GC-mass spectra as the metabolite. The tentative pathway and the biological significance of dioxane metabolism are discussed.

Animals↗
PubMed1988

Acute pulmonary response to cotton bract extract in monkeys: lung function and effects of mediator modifying compounds.

It is well established that cotton dust inhalation can compromise lung function in textile workers. Challenges with a water-soluble extract of cotton bract (CBE) can also induce reversible airway obstruction in healthy volunteers. We have examined the effect of inhaled CBE in nonhuman primates and have attempted to inhibit the bronchoconstrictive response with mediator modifying compounds. CBE (34 mg/ml or 100 mg/ml) was administered via IPPB for 15 minutes (15 breaths/min) in 12 intubated, anesthetized, adult male monkeys (Macaca fascicularis). Breath-by-breath determinations of pulmonary resistance, dynamic compliance (Cdyn), tidal volume, and breathing frequency were calculated from the transpulmonary pressure (esophageal balloon) and airflow signals and monitored for 2 hr postchallenge. Control challenges with distilled water were also performed in 3 monkeys with the greatest response from CBE. Five animals (42%) were found to respond to CBE with peak % changes in Cdyn greater than 45%. In 3 of these animals, we attempted to blunt the CBE response with chlorpheniramine (0.1 mg/kg i.v.) and a mast cell stabilizer lodoxamide (0.1 mg/ml aerosol). In these 3 animals the mean (+/- SD) peak % changes in Cdyn to CBE alone was -47.4 +/- 1.8. The CBE response following chlorpheneramine was -49 +/- 15.7 and following lodoxamide was -47.0 +/- 5.4. These data suggest that monkeys, like humans, can develop reproducible bronchoconstriction following an aerosol challenge with CBE. Furthermore, this bronchoconstriction in the monkey is probably not explained by the action of histamine or mediator release alone and an acute inflammatory reaction may be involved.

Animals↗
PubMed1976

The separation of partially modified lactate dehydrogenase by affinity chromatography. The specific activity of protomers?

Pig heart lactate dehydrogenase (L-lactate: NAD+ oxidoreductase, EC 1.1.1.27) was partially inactivated by reaction with phenylmaleimide. The resulting protein mixture was separated by affinity chromatography on a Sepharose-linked oxamate column yielding three distinct enzyme fractions with one, two and three out of four subunits being modified. The specific activities of these samples were lower than expected from the degree of modification, while the maximum binding capacity of NADH-oxamate related well to the number of catalytic centers modified. A possible cooperative effect in the native enzyme is discussed.

Animals↗
PubMed1977

Kinetic formulations for the oxidation and the reduction of glyoxylate by lactate dehydrogenase.

Chicken liver lactate dehydrogenase (L-lactate : NAD+ oxidoreductase, EC 1.1.1.27) irreversibly catalyses the oxidation of glyoxylate (hydrated form) (I) to oxalate (pH = 9.6) and the reduction of (non-hydrated form) (II) to glycolate (pH = 7.4). (I) attaches to the enzyme in the pyruvate binding site and (II) attaches to the enzyme at the L-lactate binding site. The oxidation of (I) (pH = 9.6) is adapted to the following mechanism: (see book). The abortive complexes, E-NADH-I and E-NAD+-II, are responsible for the inhibition by excess substrate in the reduction and oxidation systems, respectively. When lactate dehydrogenase and NAD+ are preincubated, E-NAD+- NAD+ appears and causes inhibition by excess NAD+ in the glyoxylate-lactate dehydrogenase-NAD+ and L-lactate-lactate dehydrogenase-NAD+ systems; the second NAD+ molecule attaches to the enzyme at the L-lactate binding site.

Animals↗
PubMed1995

An improved spectrophotometric assay of pyruvate dehydrogenase in lactate dehydrogenase contaminated mitochondrial preparations from human skeletal muscle.

In mitochondria-enriched preparations of human skeletal muscle, the measurement of pyruvate dehydrogenase activity, as determined by conventional spectrophotometric assay of NADH accumulation, is underestimated due to the oxidizing activity of the contaminating lactate dehydrogenase. Using a model reaction system consisting of varying mixtures of purified lactate and pyruvate dehydrogenases, we found that the presence of oxamate, a competitive inhibitor of the lactate dehydrogenase, allowed the measurement of a linear rate of pyruvate dehydrogenase activity without interference from lactate dehydrogenase. In the presence of 25 mM oxamate, this holds true up to a ratio of 30:1 for lactate to pyruvate dehydrogenases, respectively. A similar result was obtained when using human skeletal muscle mitochondria contaminated by lactate dehydrogenase. Rates of pyruvate dehydrogenase activity ranging from 50 to 120 nmol/min/mg protein could be routinely measured in such mitochondrial fractions. We concluded that the use of oxamate allows a spectrophotometric assay for pyruvate dehydrogenase activity to be utilized when screening for pyruvate dehydrogenase deficiency in mitochondria-enriched preparations of human skeletal muscle.

Animals↗
PubMed1990

Effect of histamine antagonists on myocardial carcinine metabolism during compound 48/80-induced shock.

Carcinine (beta-alanylhistamine) is an imidazole dipeptide that exists in mammalian hearts, increases cardiac contractility, and is metabolically linked to carnosine (beta-alanylhistidine), a non-mast cell histidine and histamine precursor during stress. We have previously shown that tissue carnosine levels are regulated by H1 and H2 receptors. This study evaluated the effects of H1, H2, and mast cell degranulation blockers on metabolism of carcinine and related imidazoles during shock induced by compound 48/80, a mast cell degranulator. Fifty 125-g male Sprague-Dawley rats were divided into nine ip treatment groups: saline, 48/80, lodoxamide (LOD, mast cell degranulation inhibitor), diphenhydramine (DPH, H1 antagonist), cimetidine (CIM, H2 antagonist), LOD + 48/80, CIM + 48/80, DPH + 48/80, or DPH + CIM + 48/80. Heart tissue was analyzed at 30 min by HPLC. 48/80 caused decreases in myocardial carnosine (P less than 0.01) and histidine (P less than 0.0001) levels and concomitant increases in carcinine (P less than 0.01), histamine (P less than 0.01), and 3-methylhistamine (P less than 0.05) compared to those of controls. These changes were inhibited by LOD or DPH. Treatment with CIM significantly increased myocardial carcinine levels compared to 48/80 alone (P less than 0.001) without an additional effect on the other compounds. These data indicate that carcinine is involved in the cardiac response to stress via the carnosine-histidine-histamine pathway. Compound 48/80-induced shock increases histamine metabolism via this pathway resulting in mobilization of myocardial carnosine and histidine to carcinine and histamine; this effect is increased by H2 receptor blockade.

Animals↗
PubMed1995

Preparation and characterization of a purified influenza virus neuraminidase vaccine.

Influenza virus neuraminidase (NA) has been shown to induce protective but infection-permissive immunity in experimental animals. Challenge infection following such immunization is attended by decreased viral replication and disease manifestations but is sufficient to provide antigenic stimulation and definitive immunity to the virus. The present report describes the preparation and characterization of a purified NA vaccine (NAV) used in Phase 1 (immunogenicity and toxicity) trials in humans. In essence, virion NA was isolated from detergent-disrupted virus by affinity chromatography on oxamic acid-agarose, treated with formalin and tested for its enzymatic activity and for its immunogenicity in Balb/c mice and New Zealand rabbits. The preparation was essentially free of viral hemagglutinin but contained residual NP and M1 proteins. Both dispersed and aggregated NA tetrameric heads were seen in electron micrographs. Enzymatic activity was preserved, and minimal immunogenic doses in mice and rabbits, respectively, were 3.7 and 0.027 micrograms per kg.

Animals↗