scholarly journals Allosteric regulation of phosphonoacetaldehyde hydrolase by n-butylphosphonic acid

1991 ◽  
Vol 280 (2) ◽  
pp. 557-559
Author(s):  
C Dumora ◽  
A M Lacoste ◽  
A Cassaigne ◽  
J P Mazat
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Enzyme Activity ◽  
Allosteric Regulation ◽  
Experimental Results ◽  
Low Concentrations ◽  
Allosteric Model

The effect of n-butylphosphonic acid on the activity of phosphonoacetaldehyde hydrolase from Pseudomonas aeruginosa was investigated: at low concentrations this compound appeared as an activator of the enzyme activity, whereas at higher concentrations it exhibited inhibitory properties. The experimental results were modelled according to an allosteric model involving two different classes of sites for n-butylphosphonic acid.

Serum Cholinesterase Variants: Examination of Several Differential Inhibitors, Salts, and Buffers Used to Measure Enzyme Activity

1971 ◽  
Vol 17 (3) ◽  
pp. 183-191 ◽  
Author(s):  
Philip J Garry
Keyword(s):  
Enzyme Activity ◽  
Sodium Fluoride ◽  
Phosphate Buffer ◽  
Divalent Cations ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Serum Cholinesterase ◽  
Low Concentrations

Abstract Dibucaine, used as a differential inhibitor with acetyl-, propionyl-, and butyrylthiocholine as substrate, clearly identified the "usual" and "atypical" serum cholinesterases. Succinylcholine was also used successfully as a differential inhibitor with butyrylthiocholine as substrate. Sodium fluoride, used as a differential inhibitor, gave conflicting results, depending on whether Tris or phosphate buffer was used in the assay. Mono- and divalent cations (NaCl, KCl, MgCl2, CaCl2, and BaCl2) activated the "usual" and inhibited the "atypical" enzyme at low concentrations. The "usual" enzyme had the same activity in 0.05 mol of Tris or phosphate buffer per liter, while the heterozygous and "atypical" enzymes showed 12 and 42% inhibition, respectively, when assayed in the phosphate buffer. Kinetic studies showed the phosphate acted as a competitive inhibitor of "atypical" enzyme. Km values, determined for "usual" and "atypical" enzymes, were 0.057 and 0.226 mmol/liter, respectively, with butyrylthiocholine as substrate.

scholarly journals Detection of endotoxins with the Limulus test in burned and unburned mice infected with different species of gramnegative bacteria

1975 ◽  
Vol 75 (1) ◽  
pp. 99-112 ◽  
Author(s):  
R. J. Jones ◽  
E. A. Roe ◽  
R. E. Dyster
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Low Concentrations ◽  
High Concentrations ◽  
Very High ◽  
Limulus Test

SUMMARYThe Limulus test detected endotoxins in the plasma of burned and unburned mice infected with different species of gram-negative bacteria. Individual strains of different species of gram-negative bacteria produced different amounts of endotoxin in the plasma of infected mice. Plasma from mice given lethal infections showed very high concentrations of endotoxin. Low concentrations of endotoxin in the plasma were tolerated by mice but high concentrations were invariably fatal. A polyvalent pseudomonas vaccine reduced endotoxin in the plasma of mice given lethal infections of Pseudomonas aeruginosa.

EGTA-sensitive and -insensitive forms of particulate adenylate cyclase in rat cerebral cortex: regulation by divalent cations and GTP

1985 ◽  
Vol 63 (8) ◽  
pp. 1007-1016 ◽  
Author(s):  
P. V. Sulakhe
Keyword(s):  
Enzyme Activity ◽  
Cerebral Cortex ◽  
Adenylate Cyclase ◽  
Gray Matter ◽  
Rank Order ◽  
Divalent Cations ◽  
Rat Cerebral Cortex ◽  
Chloride Salt ◽  
Low Concentrations ◽  
Stimulation Of

Interactions of several divalent cations (Mn2+, Ca2+, Co2+, Sr2+, and Zn2+) with EGTA-inhibitable adenylate cyclase were investigated in washed membranes (particles) isolated from the gray matter of rat cerebral cortex. The EGTA-inhibitable (called sensitive) enzyme activity was assayed in the presence of Triton X-100 since this detergent caused a marked increase (up to 20-fold) in the enzyme activity. The effects of various divalent metals (all added as chloride salt) indicated the presence of two distinct sites called site I and site II. At low concentrations (less than micromolar) Mn2+, Co2+, and Ca2+ increased (up to 10-fold) the enzyme activity to the same extent and appeared to act via binding to site I (high affinity site). The rank order of affinity was Mn2+ ≥ Co2+ > Ca2+. Zn2+ showed the highest affinity and Sr2+ the lowest towards binding to site I; both these metals increased the enzyme activity to lesser extents than Mn2+, Co2+, or Ca2+. GTP was not required for the stimulation of this enzyme by low concentrations of Ca2+. The interaction of Mn2+ with site II (low affinity site) caused further increase in the enzyme activity, whereas Co2+, Ca2+, and Sr2+ were inhibitory at concentrations >10 μM. Isolated fraction contained loosely and tightly associated pools of calmodulin. Myelin basic protein, but not calcineurin, inhibited the EGTA-sensitive adenylate cyclase activity. The EGTA-insensitive enzyme activity was increased by norepinephrine by mechanisms that depended on GTP and was inhibited by Ca2+. The stimulation of the EGTA-insensitive enzyme modulated the Mg2+ requirement such that Mg2+ binding to the low affinity site (site II) apparently occurred with higher affinity. The likely significance of these results is discussed with regard to (i) the presence of two classes of adenylate cyclase in rat cerebral cortex gray matter and (ii) the regulation of their activities by calmodulin-requiring and GTP-requiring mechanisms.

scholarly journals Coproporphyrinogenase in tobacco (Nicotiana tabacum L.)

1970 ◽  
Vol 117 (2) ◽  
pp. 215-220 ◽  
Author(s):  
W. P. Hsu ◽  
G. W. Miller
Keyword(s):  
Enzyme Activity ◽  
Nicotiana Tabacum ◽  
Differential Centrifugation ◽  
Enzyme Protein ◽  
Sodium Amalgam ◽  
Low Concentrations ◽  
Nicotiana Tabacum L ◽  
Km Value ◽  
Ammonium Sulphate Fractionation ◽  
Final Purification

1. Coproporphyrinogenase was extracted and purified from tobacco (Nicotiana tabacum L.). Enzyme activity was mainly located in mitochondria rather than in chloroplasts. The enzyme was purified by differential centrifugation, ammonium sulphate fractionation, calcium phosphate gel adsorption and dialysis. A 69-fold final purification was obtained. 2. An apparent Km value of 3.6×10−5m was found, the value being largely dependent on the amount of coproporphyrin III recovered after reduction with sodium amalgam to coproporphyrinogen III. Protoporphyrin formation was linear up to 3h and decreased with further incubation. The enzyme activity increased with the concentration of enzyme protein up to 30μg/ml of solution. 3. Enzyme activity was greatly enhanced by increasing Fe2+ concentrations up to 0.5mm, beyond which inhibition occurred. Co2+ and Mn2+ were also found to activate at low concentrations (0.1mm) and inhibit at higher concentrations (5mm). Fe3+ and Cu2+, both at 0.1mm, and o-phenanthroline and EDTA, each at 1mm, were found to be inhibitory.

The temperature variation of diamagnetic susceptibility

1954 ◽  
Vol 222 (1149) ◽  
pp. 239-253 ◽  
Keyword(s):  
Magnetic Properties ◽  
Fermi Surface ◽  
Temperature Variation ◽  
Diamagnetic Susceptibility ◽  
Experimental Results ◽  
Temperature Dependent ◽  
Constant Energy ◽  
Low Concentration ◽  
Low Concentrations ◽  
Theoretical Results

The temperature variation of a major contribution to the diamagnetic susceptibility of orbital electrons is calculated for various forms of the surfaces of constant energy in the neighbourhood of the Fermi surface in k space. Both quadratic and non-quadratic ϵ , k relations are considered. A discussion is given of the theoretical results in relation to the relevant experimental results and, in particular, in relation to the complicated variations of susceptibility with ( a ) temperature and ( b ) concentration for alloys of bismuth with low concentrations of added lead and tellurium. It is shown that the treatment provides a basis for a simple and direct correlation of the temperature-dependent and concentration-dependent magnetic properties for low-concentration diamagnetic alloy sequences.

scholarly journals Specific alkylation of a histidine residue in carnitine acetyltransferase by bromoacetyl-l-carnitine

1970 ◽  
Vol 116 (4) ◽  
pp. 713-720 ◽  
Author(s):  
J. F. A. Chase ◽  
P. K. Tubbs
Keyword(s):  
Enzyme Activity ◽  
Alkylation Reaction ◽  
Histidine Residue ◽  
Carnitine Acetyltransferase ◽  
Irreversible Loss ◽  
Total Acid ◽  
Active Centre ◽  
Low Concentrations ◽  
Spontaneous Hydrolysis ◽  
Hydrolysis Of

Incubation of carnitine acetyltransferase with low concentrations of bromoacetyl-l-carnitine causes a rapid and irreversible loss of enzyme activity; one mol of inhibitor can inactivate one mol of enzyme. Bromoacetyl-d-carnitine, iodoacetate or iodoacetamide are ineffective. l-Carnitine protects the transferase from bromoacetyl-l-carnitine. Investigation shows that the enzyme first reversibly binds bromoacetyl-l-carnitine with an affinity similar to that shown for the normal substrate acetyl-l-carnitine; this binding is followed by an alkylation reaction, forming the carnitine ester of a monocarboxymethyl-protein, which is catalytically inactive. The carnitine is released at an appreciable rate by spontaneous hydrolysis, and the resulting carboxymethyl-enzyme is also inactive. Total acid hydrolysis of enzyme after treatment with 2-[14C]bromoacetyl-l-carnitine yields N-3-carboxy[14C]methylhistidine as the only labelled amino acid. These findings, taken in conjunction with previous work, suggest that the single active centre of carnitine acetyltransferase contains a histidine residue.

scholarly journals The activation of aldehyde dehydrogenase by diethylstilboestrol and 2,2′-dithiodipyridine

1982 ◽  
Vol 207 (1) ◽  
pp. 81-89 ◽  
Author(s):  
T M Kitson
Keyword(s):  
Enzyme Activity ◽  
Aldehyde Dehydrogenase ◽  
Human Liver ◽  
Common Property ◽  
Rabbit Liver ◽  
Aldehyde Dehydrogenases ◽  
Cytoplasmic Enzyme ◽  
Sheep Liver ◽  
Low Concentrations ◽  
Liver Aldehyde Dehydrogenase

1. The activation of sheep liver cytoplasmic aldehyde dehydrogenase by diethylstilboestrol and by 2,2′-dithiodipyridine is described. The effects of the two modifiers are very similar with respect to variation with acetaldehyde concentration, pH and temperature. Thus the degree of activation is maximal when the enzyme is assayed at approx. 1 mM-acetaldehyde, is greater at 25 degrees C than at 37 degrees C, and is greater at pH 7.4 than at pH 9.75. With low concentrations of acetaldehyde both modifiers decrease the enzyme activity. 2. Diethylstilboestrol affects the sheep liver cytoplasmic enzyme in a very similar way to that previously described for a rabbit liver cytoplasmic enzyme. Preliminary experiments show that the same is true for a preparation of human liver aldehyde dehydrogenase. It is proposed that sensitivity to diethylstilboestrol (and steroids) is a common property of all mammalian cytoplasmic aldehyde dehydrogenases.

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