Kinetic studies of mutant human erythrocyte adenine phosphoribosyltransferases

1968 ◽  
Vol 46 (7) ◽  
pp. 703-706 ◽  
Author(s):  
J. Frank Henderson ◽  
Helen R. Miller ◽  
William N. Kelley ◽  
Frederick M. Rosenbloom ◽  
J. Edwin Seegmiller
Keyword(s):  
Reaction Mechanism ◽  
Human Erythrocyte ◽  
Enzyme Activities ◽  
Kinetic Studies ◽  
Kinetic Constants ◽  
Heat Inactivation ◽  
Adenine Phosphoribosyltransferase ◽  
Michaelis Constants ◽  
Low Degrees ◽  
Reduced Activity

The kinetic constants and reaction mechanism of human erythrocyte adenine phosphoribosyltransferase from individuals whose enzyme activities have high, intermediate, or low degrees of stability to heat inactivation, and in a human mutant with reduced activity of this enzyme, have been measured. The Michaelis constants for one or both substrates are different from normal in seven mutants.

scholarly journals Kinetic studies of nitrogenase from soya-bean root-nodule bacteroids

1973 ◽  
Vol 131 (1) ◽  
pp. 61-75 ◽  
Author(s):  
F. J. Bergersen ◽  
G. L. Turner
Keyword(s):  
Reaction Mechanism ◽  
Protein Concentration ◽  
Root Nodule ◽  
Maximum Velocity ◽  
Kinetic Studies ◽  
Soya Bean ◽  
Michaelis Constant ◽  
Fe Protein ◽  
Catalytic Sites ◽  
Michaelis Constants

The apparent Michaelis constants [K′(N2) and K′(C2H2)] and the corresponding apparent maximum velocity values (V′) for soya-bean bacteroid nitrogenase increased concomitantly in response to increases in nitrogenase Fe–protein concentration and ATP concentration in cell-free assays and in response to O2 pressure in intact nodules and bacteroid suspensions. K′(C2H2) in cell-free assays was also affected by pH and by Na2S2O4 concentration. Nitrogenase Fe–protein behaved as a catalytic effector reacting at interacting sites on the nitrogenase Fe–Mo–protein. The results indicated that the Fe–Mo–protein probably bears the catalytic sites for N2 and C2H2 reduction. It is concluded that reduction of N2 or C2H2 by this nitrogenase involves a reaction mechanism with a sequence of unknown order. The sequence in which substrate, enzyme, effector, ATP and reductant react determines which of the various rate-constants are involved in the apparent Michaelis constant, whose true kinetic meaning was thus unresolved.

Ligand-Enabled γ-C(sp3)–H Olefination of Free Carboxylic Acids

2020 ◽  
Author(s):  
Kiron Kumar Ghosh ◽  
Alexander Uttry ◽  
Francesca Ghiringhelli ◽  
Arup Mondal ◽  
Manuel van Gemmeren
Keyword(s):  
Reaction Mechanism ◽  
Carboxylic Acids ◽  
Michael Addition ◽  
Kinetic Studies ◽  
Wide Range ◽  
Palladium Catalyzed

We report the ligand enabled C(sp3)–H activation/olefination of free carboxylic acids in the γ-position. Through an intramolecular Michael-addition, δ-lactones are obtained as products. Two distinct ligand classes are identified that enable the challenging palladium-catalyzed activation of free carboxylic acids in the γ-position. The developed protocol features a wide range of acid substrates and olefin reaction partners and is shown to be applicable on a preparatively useful scale. Insights into the underlying reaction mechanism obtained through kinetic studies are reported.<br>

scholarly journals Aspartate aminotransferase. The effects of ionic concentration on kinetic constants of both isoenzymes

1968 ◽  
Vol 106 (3) ◽  
pp. 581-586 ◽  
Author(s):  
T. R. C. Boyde
Keyword(s):  
Aspartate Aminotransferase ◽  
Specific Effect ◽  
Ionic Concentration ◽  
Phosphate Concentration ◽  
Kinetic Constants ◽  
Sharp Minimum ◽  
Ionic Concentrations ◽  
Michaelis Constants ◽  
Added Salt

1. The Michaelis constants for both isoenzymes for both substrates depend strongly on ionic concentration, being approximately proportional to phosphate concentration over considerable ranges. This is probably an effect of anions only. 2. In the absence of added salt, Km (2-oxoglutarate) (anionic isoenzyme) is so small as to be indeterminate. 3. Km (l-aspartate) (anionic isoenzyme) passes through a sharp minimum at about 3·3mm-phosphate. It is not clear whether this is a specific effect of phosphate. 4. Both substrates are inhibitory at sufficiently low ionic concentrations. 5. A modified graphical procedure is described for the derivation of the kinetic constants.

From the Understanding of the Reaction Mechanism Towards Optimizing the Deposition Rate and Optoelectronic Properties of a-Si:H

1989 ◽  
Vol 149 ◽  
Author(s):  
S. Veprek ◽  
M. Heintze ◽  
R. Bayer ◽  
N. Jurčik-Rajman
Keyword(s):  
Reaction Mechanism ◽  
Surface Coverage ◽  
Kinetic Studies ◽  
Reactive Intermediates ◽  
Sticking Coefficient ◽  
High Quality ◽  
Rate Determining Step ◽  
Homogeneous Good ◽  
Good Agreement

ABSTRACTWe present new results of kinetic studies of the deposition of high quality a-Si:H which strongly support the reaction mechanism suggested in our earlier papers: 1. SiH4 → SiH2; 2. SiH2 + SiS4 → Si2H6 (SiH2 + Si2H6 → Si3H6); 3. Si2H6 → 2a-Si:H (Si3H8 → 3a-Si:H). The “SiH3 mechanism”, as promoted by several workers, is in contradiction with these experimental facts.The di- and trisilane, which have a much higher reactive sticking coefficient than monosilane, play the role of reactive intermediates which facilitate the heterogeneous decomposition of silicon carrying species at the surface of the growing film. The values of the reactive sticking coefficient of Si2H6 and Si3H8 depend on the surface coverage by chemisorbed hydrogen; they increase with decreasing surface coverage. Under the conditions of the growth of high quality a-Si:H films the reactive sticking coefficient of disilane amounts to 10−4 to 10−2 which is in a good agreement with recent data of other authors.The rate determining step of the growth of high quality a-Si:H films is the desorption of hydrogen from the surface of the growing film. This can be strongly enhanced by ion bombardment at impact energy of <100 eV. In this way, homogeneous, good quality films were deposited at rates up to 1800 Angströms/min, and there is a well justified hope that this rate can be further increased.

New short-term heat inactivation method of cytomegalovirus (CMV) in breast milk: impact on CMV inactivation, CMV antibodies and enzyme activities

2019 ◽  
Vol 104 (6) ◽  
pp. F604-F608 ◽  
Author(s):  
Jens Maschmann ◽  
Denise Müller ◽  
Katrin Lazar ◽  
Rangmar Goelz ◽  
Klaus Hamprecht
Keyword(s):  
Breast Milk ◽  
Enzyme Activities ◽  
Primary Source ◽  
Wild Type Virus ◽  
Heat Inactivation ◽  
Target Cells ◽  
Igg Antibodies ◽  
Wild Type ◽  
Short Term ◽  
Milk Whey

ObjectivesBreast milk (BM) is the primary source of cytomegalovirus (CMV) transmission to premature infants with potentially harmful consequences. We therefore wanted to evaluate temperature and duration of short-term BM pasteurisation with respect to CMV inactivation, effect on CMV-IgG antibodies and BM enzyme activities.Methods116 artificially CMV-spiked BM and 15 wild-type virus-infected samples were subjected for 5 s to different temperatures (55°C–72°C). CMV-IE-1 expression in fibroblast nuclei was assessed using the milk whey fraction in short-term microculture. BM lipase and alkaline phosphatase (AP) activities and CMV binding using CMV-recomLine immunoblotting and neutralising antibodies using epithelial target cells were analysed before and after heating.ResultsA minimum of 5 s above 60°C was necessary for CMV inactivation in both CMV-AD-169 spiked and wild-type infected BM. Lipase was very heat sensitive (activities of 54% at 55°C, 5% at 60°C and 2% at 65°C). AP showed activities of 77%, 88% and 10%, respectively. CMV-p150 IgG antibodies were mostly preserved at 62°C for 5 s.ConclusionOur results show that short-term pasteurisation of BM at 62°C for 5 s might be efficient for CMV inactivation and reduces loss of enzyme activities, as well as CMV binding, and functional CMV antibodies.

Mechanisms of inhibition of adenine phosphoribosyltransferase by adenine nucleosides and nucleotides

1970 ◽  
Vol 48 (5) ◽  
pp. 573-579 ◽  
Author(s):  
J. Frank Henderson ◽  
R. E. A. Gadd ◽  
H. M. Palser ◽  
M. Hori
Keyword(s):  
Adenosine Triphosphate ◽  
Kinetic Studies ◽  
Adenosine Diphosphate ◽  
Free Enzyme ◽  
Adenine Phosphoribosyltransferase ◽  
Enzyme Form

Kinetic studies of the inhibition of adenine phosphoribosyltransferase by adenine 6′-deoxyallofuranoside and 2′-deoxyadenylate indicate that both compounds bind to free enzyme and to the enzyme–phosphoribosylpyrophosphate complex, although they bind with different relative affinities to each enzyme form. The sites to which these inhibitors bind appear to be different from those to which substrates and products bind. Kinetic and physical studies show that adenosine diphosphate and adenosine triphosphate also bind to several enzyme forms, and that their mechanisms of inhibition of this enzyme are complex.

CHARACTERIZATION OF HUMAN OVARIAN OESTRADIOL-17β OXIDOREDUCTASE ACTIVITY

1977 ◽  
Vol 85 (3) ◽  
pp. 624-635 ◽  
Author(s):  
Donald E. Pittaway ◽  
Richard N. Andersen ◽  
James R. Givens
Keyword(s):  
Enzyme Activity ◽  
Enzyme Activities ◽  
Enzyme Preparation ◽  
Phenolic Hydroxyl ◽  
Supernatant Fraction ◽  
Oxidoreductase Activity ◽  
Sulfhydryl Reagent ◽  
Michaelis Constants ◽  
Human Ovaries

ABSTRACT Oestradiol-17β oxidoreductase activity, which catalyzes the interconversion of oestrone and oestradiol, was investigated in preparations of human ovaries. The enzyme activities were localized primarily in the 105 000 × g supernatant fraction; dialyzed supernatant preparations were used in subsequent studies. The pH optima were 6.9 for reduction and 8.1 for 17β-dehydrogenation. The apparent Michaelis constants for oestrone and oestradiol were 1 × 10-7 m and 5 × 10-7 m, respectively. The enzyme activity was present with either NADP(H) or NAD(H), though NADP(H) were the preferred cofactors. Non-aromatic steroids androstenedione, dehydroepiandrosterone, testosterone and 5-androstene-3β,17β-diol were poor substrates for the enzyme preparation. Methylation of the phenolic hydroxyl of oestrone and oestradiol resulted in slightly enhanced activities. The sulfhydryl reagent, N-ethylmaleimide, inhibited the reduction of oestrone. A dialyzed supernatant preparation retained approximately 79 % of the original enzyme activity when stored at −20°C for 6 weeks.

Sign in / Sign up

Export Citation Format

Share Document