scholarly journals The kinetic properties and reaction mechanism of histamine methyltransferase from human skin

1980 ◽  
Vol 187 (3) ◽  
pp. 819-828 ◽  
Author(s):  
D M Francis ◽  
M F Thompson ◽  
M W Greaves
Keyword(s):  
Reaction Mechanism ◽  
Human Skin ◽  
Substrate Inhibition ◽  
Kinetic Properties ◽  
Sequential Reaction ◽  
Methyl Group ◽  
Michaelis Constants ◽  
Histamine Methyltransferase ◽  
The Mean ◽  
Inhibited Enzyme

The substrate kinetic properties of histamine methyltransferase from human skin were studied at limiting concentrations of both histamine and S-adenosylmethionine. Substrate inhibition by histamine was observed at concentrations above 10 microM. Primary plots showed evidence of a sequential reaction mechanism. The Michaelis constants were derived from secondary plots of slopes from the primary plots ([S]/v versus [S]) versus reciprocal of the second substrate concentration. The mean Km values for histamine and S-adenosylmethionine were 4.2 and 1.8 microM respectively. Histamine in concentrations of 25-100 microM inhibited enzyme activity uncompetitively with respect to S-adenosylmethionine. No substrate inhibition was observed with S-adenosylmethionine. To elucidate the reaction mechanism further, inhibition by the two products, S-adenosylhomocysteine and 1-methylhistamine, was studied. S-Adenosylhomocysteine inhibited non-competitively with respect to histamine and competitively with respect to S-adenosylmethionine. 1-Methylhistamine inhibited non-competitively with respect to histamine and to S-adenosylmethionine. These results are interpreted as providing evidence for an ordered sequential Bi Bi reaction mechanism, with the methyl-group donor S-adenosylmethionine as the first substrate that adds to the enzyme and histamine as the second substrate. 1-Methylhistamine is the first product to leave the enzyme and S-adenosylhomocysteine is the second. The results are discussed in terms of the possible role that this enzyme could play in the modulation of histamine-mediated reactions in skin.

scholarly journals Kinetic properties of spermine synthase from bovine brain

1983 ◽  
Vol 215 (3) ◽  
pp. 669-676 ◽  
Author(s):  
R L Pajula
Keyword(s):  
Initial Velocity ◽  
Substrate Inhibition ◽  
Product Inhibition ◽  
Bovine Brain ◽  
Kinetic Properties ◽  
Methylthioadenosine Phosphorylase ◽  
Spermine Synthase ◽  
Michaelis Constants ◽  
Inhibition Studies ◽  
Competitive Product

A kinetic analysis including initial-velocity and product-inhibition studies were performed with spermine synthase purified from bovine brain. The enzyme activity was assayed in the presence of 5′-methylthioadenosine phosphorylase as an auxiliary enzyme to prevent the accumulation of the inhibitory product, 5′-methylthioadenosine, and thus to obtain linearity of the reaction with time. Initial-velocity studies gave intersecting or converging linear double-reciprocal plots. No substrate inhibition by decarboxylated S-adenosylmethionine was observed at concentrations up to 0.4 mM. Apparent Michaelis constants were 60 microM for spermidine and 0.1 microM for decarboxylated S-adenosylmethionine. Spermine was a competitive product inhibitor with respect to decarboxylated S-adenosylmethionine, but a mixed one with respect to the other substrate, spermidine. 5′-Methylthioadenosine showed a mixed inhibition with both substrates, predominantly competitive with respect to decarboxylated S-adenosylmethionine and predominantly uncompetitive with respect to spermidine. The observed kinetic and inhibition patterns are consistent with a compulsory-order mechanism, where both substrates add to the enzyme before products can be released.

scholarly journals Pyrolysis Kinetic Properties of Thermal Insulation Waste Extruded Polystyrene by Multiple Thermal Analysis Methods

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5595
Author(s):  
Ang Li ◽  
Wenlong Zhang ◽  
Juan Zhang ◽  
Yanming Ding ◽  
Ru Zhou
Keyword(s):  
Reaction Mechanism ◽  
Thermal Insulation ◽  
Conversion Rate ◽  
Model Fitting ◽  
Pso Algorithm ◽  
Energy Utilization ◽  
Kinetic Properties ◽  
Insulation Material ◽  
Heating Rates ◽  
Model Free

Extruded polystyrene (XPS) is a thermal insulation material extensively applied in building systems. It has attracted much attention because of outstanding thermal insulation performance, obvious flammability shortcoming and potential energy utilization. To establish the reaction mechanism of XPS’s pyrolysis, thermogravimetric experiments were performed at different heating rates in nitrogen, and multiple methods were employed to analyze the major kinetics of pyrolysis. More accurate kinetic parameters of XPS were estimated by four common model-free methods. Then, three model-fitting methods (including the Coats-Redfern, the iterative procedure and masterplots method) were used to establish the kinetic model. Since the kinetic models established by the above three model-fitting methods were not completely consistent based on different approximations, considering the effect of different approximates on the model, the reaction mechanism was further established by comparing the conversion rate based on the model-fitting methods corresponding to the possible reaction mechanisms. Finally, the accuracy of the above model-fitting methods and Particle Swarm Optimization (PSO) algorithm were compared. Results showed that the reaction function g(α) = (1 − α)−1 − 1 might be the most suitable to characterize the pyrolysis of XPS. The conversion rate calculated by masterplots and PSO methods could provide the best agreement with the experimental data.

Effects of temperature on measurement of alkaline phosphatase activity.

1985 ◽  
Vol 31 (2) ◽  
pp. 185-190 ◽  
Author(s):  
W H Copeland ◽  
D A Nealon ◽  
R Rej
Keyword(s):  
Alkaline Phosphatase ◽  
Phosphatase Activity ◽  
Kinetic Properties ◽  
Porcine Kidney ◽  
Human Origin ◽  
Arrhenius Behavior ◽  
Nitrophenyl Phosphate ◽  
Activity Measurements ◽  
Michaelis Constants ◽  
Effects Of Temperature

Abstract We examined the effects of temperature on the activity and steady-state kinetic properties of alkaline phosphatase (EC 3.1.3.1). Purified isoenzymes from human liver, intestine, and placenta were used, as was human serum, and the enzyme from porcine kidney. Phosphatase activity was estimated by two different assay techniques. For all isoenzymes, apparent Michaelis constants for the substrate 4-nitrophenyl phosphate decreased with increased temperature; Km at 37 degrees C was typically half that determined at 25 degrees C. All enzymes of human origin exhibited similar linear Arrhenius relationships over the range examined, 20-37 degrees C (Ea of 30-36 kJ X mol-1). The porcine kidney enzyme obeyed an Arrhenius relationship that was slightly, but significantly, different from the isoenzymes of human origin. Temperature relationships based upon Arrhenius behavior and individual activity measurements are presented. For human alkaline phosphatases, they differed by no more than 10%.

scholarly journals Crystal structure of dichlorido{4-[(E)-(methoxyimino-κN)methyl]-1,3-thiazol-2-amine-κN3}palladium(II)

2015 ◽  
Vol 71 (1) ◽  
pp. m10-m11 ◽  
Author(s):  
Viktorita V. Dyakonenko ◽  
Olga O. Zholob ◽  
Svitlana I. Orysyk ◽  
Vasily I. Pekhnyo
Keyword(s):  
Bidentate Ligand ◽  
The Other ◽  
Mean Deviation ◽  
Amino Group ◽  
Methyl Group ◽  
Square Planar ◽  
The Mean ◽  
Van Der Waals Radii ◽  
Cl Atoms ◽  
Coordination Plane

In the title compound, [PdCl2(C5H7N3OS)], the PdIIatom adopts a distorted square-planar coordination sphere defined by two N atoms of the bidentate ligand and two Cl atoms. The mean deviation from the coordination plane is 0.029 Å. The methyl group is not coplanar with the plane of the metallacycle [torsion angle C—O—N—C = 20.2 (4)°]. Steric repulsion between the methyl group and atoms of the metallacycle is manifested by shortened intramolecular H...C contacts of 2.27, 2.38 and 2.64 Å, as compared with the sum of the van der Waals radii of 2.87 Å. The amino group participatesviaone H atom in the formation of an intramolecular N—H...Cl hydrogen bond. In the crystal, the other H atom of the amino group links moleculesviabifurcated N—H...(Cl,O) hydrogen bonds into chains parallel to [001].

scholarly journals Purification and kinetic properties of ox brain histamine N-methyltransferase

1986 ◽  
Vol 233 (3) ◽  
pp. 669-676 ◽  
Author(s):  
W L Gitomer ◽  
K F Tipton
Keyword(s):  
Acetic Acid ◽  
Steady State ◽  
Mouse Brain ◽  
Initial Rate ◽  
Substrate Inhibition ◽  
Gel Filtration ◽  
Product Inhibition ◽  
Kinetic Properties ◽  
Brain Histamine ◽  
Inhibition Studies

Histamine N-methyltransferase (EC 2.1.1.8) was purified 1100-fold from ox brain. The native enzyme has an Mr of 34800 +/- 2400 as measured by gel filtration on Sephadex G-100. The enzyme is highly specific for histamine. It does not methylate noradrenaline, adrenaline, DL-3,4-dihydroxymandelic acid, 3,4-dihydroxyphenylacetic acid, 3-hydroxytyramine or imidazole-4-acetic acid. Unlike the enzyme from rat and mouse brain, ox brain histamine N-methyltransferase did not exhibit substrate inhibition by histamine. Initial rate and product inhibition studies were consistent with an ordered steady-state mechanism with S-adenosylmethionine being the first substrate to bind to the enzyme and N-methylhistamine being the first product to dissociate.

scholarly journals GC×GC measurements of C<sub>7</sub>-C<sub>11</sub> aromatic and n-alkane hydrocarbons on Crete, in air from Eastern Europe during the MINOS campaign

2003 ◽  
Vol 3 (5) ◽  
pp. 1461-1475 ◽  
Author(s):  
X. Xu ◽  
C. Williams ◽  
H. Plass-Dülmer ◽  
H. Berresheim ◽  
G. Salisbury ◽  
...  
Keyword(s):  
Rate Constants ◽  
Field Measurements ◽  
Early Morning ◽  
Reaction Model ◽  
Sequential Reaction ◽  
Related Data ◽  
Mixing Ratios ◽  
Ground Station ◽  
The Mean ◽  
The Relationship

Abstract. During the Mediterranean Intensive Oxidant Study (MINOS) campaign in August 2001 gas-phase organic compounds were measured using comprehensive two-dimensional gas chromatography (GCxGC) at the Finokalia ground station, Crete. In this paper, C7-C11 aromatic and n-alkane measurements are presented and interpreted. The mean mixing ratios of the hydrocarbons varied from 1±1 pptv (i-propylbenzene) to 43±36 pptv (toluene). The observed mixing ratios showed strong day-to-day variations and generally higher levels during the first half of the campaign. Mean diel profiles showed maxima at local midnight and late morning, and minima in the early morning and evening. Results from analysis using a simplified box model suggest that both the chemical sink (i.e. reaction with OH) and the variability of source strengths were the causes of the observed variations in hydrocarbon mixing ratios. The logarithms of hydrocarbon concentrations were negatively correlated with the OH concentrations integral over a day prior to the hydrocarbon measurements. Slopes of the regression lines derived from these correlations for different compounds are compared with literature rate constants for their reactions with OH. The slopes for most compounds agree reasonably well with the literature rate constants. A sequential reaction model has been applied to the interpretation of the relationship between ethylbenzene and two of its potential products, i.e. acetophenone and benzeneacetaldehyde. The model can explain the good correlation observed between [acetophenone]/[ethylbenzene] and [benzeneacetaldehyde]/[ethylbenzene]. The model results and field measurements suggest that the reactivity of benzeneacetaldehyde may lie between those of acetophenone and ethylbenzene and that the ratio between yields of acetophenone and benzeneacetaldehyde may be up to 28:1. Photochemical ages of trace gases sampled at Finokalia during the campaign are estimated using the sequential reaction model and related data. They lie in the range of about 0.5-2.5 days.

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