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.

scholarly journals The temperature-dependence of adenylate cyclase from baker's yeast

1979 ◽  
Vol 181 (3) ◽  
pp. 539-543 ◽  
Author(s):  
J Londesborough ◽  
K Varimo
Keyword(s):  
Reaction Mechanism ◽  
Adenylate Cyclase ◽  
Temperature Dependence ◽  
Reaction Rate ◽  
Arrhenius Plot ◽  
Maximum Velocity ◽  
Michaelis Constant ◽  
Arrhenius Plots ◽  
Temperature Range ◽  
Membrane Bound

The Michaelis constant of membrane-bound adenylate cyclase increased from 1.1 to 1.8 mM between 7 and 38 degrees C (delta H = 13 kJ/mol). Over this temperature range, the maximum velocity increased 10-fold, and the Arrhenius plot was nearly linear, with an average delta H* of 51 kJ/mol. The temperature-dependence of the reaction rate at 2 mM-ATP was examined in more detail: for Lubrol-dispersed enzyme, Arrhenius plots were nearly linear with average delta H* values of 45 and 68 kJ/mol, respectively, for untreated and gel-filtered enzymes; for membrane-bound enzyme, delta H changed from 40 kJ/mol above about 21 degrees C to 62 kJ/mol below 21 degrees C, but this behaviour does not necessarily indicate an abrupt, lipid-induced, transition in the reaction mechanism.

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.

The O-methylation of catechol oestrogens by pig conceptuses and endometrium during the peri-implantation period

1990 ◽  
Vol 127 (1) ◽  
pp. 77-84 ◽  
Author(s):  
C. Chakraborty ◽  
D. L. Davis ◽  
S. K. Dey
Keyword(s):  
Maximum Velocity ◽  
Kinetic Studies ◽  
Synthetic Activity ◽  
Hydroxylase Activity ◽  
Michaelis Constant ◽  
Comt Activity ◽  
Implantation Period

ABSTRACT Pig conceptuses display a surge in oestrogen and catecholoestrogen synthetic activity during the periimplantation period. However, the pathways of catecholoestrogen metabolism in pig conceptuses and endometrium are unknown. O-Methylation is an important route of catecholoestrogen metabolism. Therefore, the O-methylations of 2- and 4-hydroxy-oestradiols (2- and 4-OH-oestradiol) by cytosol of pig conceptuses and endometrium during the periimplantation period were studied. Kinetic studies performed in tissues obtained on day 13 of pregnancy (day 0 = first acceptance of the male) indicated that the O-methylation of 2-OH-oestradiol displayed simple Michaelis–Menten kinetics in both tissues. In blastocysts, the apparent Michaelis constant (Km) and maximum velocity (Vmax) for the O-methylation of 2-OH-oestradiol were 1·4 μmol/l and 11·27 pmol/mg protein per min respectively, and when 4-OH-oestradiol was used as substrate, the values were 2·53 μmol/l and 9·86 pmol/mg protein per min respectively. The apparent Km and Vmax values for the O-methylation of 2-OH-oestradiol in endometrium were 0·77 μmol/l and 19·6 pmol/mg protein per min respectively, and for the O-methylation of 4-OH-oestradiol were 2·44 μmol/l and 10·38 pmol/mg protein per min respectively. Ontogenesis of catechol-O-methyltransferase (COMT) in conceptuses and endometrium was studied from day 10 to day 19 of pregnancy. Conceptus COMT activity was lowest on day 10 and increased gradually to day 19 of pregnancy. Because a surge of oestradiol-2/4-hydroxylase activity occurs on days 11–13, less COMT activity on these days than on the later days of pregnancy is consistent with a role for catecholoestrogens in conceptus-maternal signalling during pregnancy establishment. Endometrial COMT activity on day 10 was higher than that on later days of pregnancy. Therefore, a role for COMT in modulation of catecholoestrogen and oestrogen function during the peri-implantation period is possible. Journal of Endocrinology (1990) 127, 77–84

scholarly journals Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

1970 ◽  
Vol 120 (4) ◽  
pp. 809-814 ◽  
Author(s):  
F. J. Ballard
Keyword(s):  
Rat Liver ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Mitochondrial Enzymes ◽  
High Concentration ◽  
Michaelis Constant ◽  
Bivalent Cation ◽  
Sheep Liver ◽  
Michaelis Constants

1. Measurements of Michaelis constants for oxaloacetate in the reaction catalysed by liver phosphoenolpyruvate carboxykinase give values much lower than previously reported. With Mg2+ as bivalent cation, the Michaelis constant was approx. 2.5×10−5m whether the enzyme used was the mitochondrial phosphoenolpyruvate carboxykinase purified from sheep liver or chicken liver or the cytosol enzyme purified from rat liver or sheep liver. 2. When Mn2+ replaced Mg2+ in the reaction a lower Michaelis constant of 9×10−6m was found, but only with the mitochondrial enzymes. 3. With all enzymes malate at high concentration was a competitive inhibitor with respect to oxaloacetate when Mn2+ was the added cation. With Mg2+ the inhibition by malate was competitive with the mitochondrial enzymes and non-competitive with the cytosol enzymes.

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>

Peroxidases from Tulip Bulbs (Tulipa fosteriana, L.) Oxidize Xenobiotics NNitrosodimethylamine and N-Nitroso-N-methylaniline in vitro

1997 ◽  
Vol 62 (11) ◽  
pp. 1804-1814 ◽  
Author(s):  
Marie Stiborová ◽  
Hana Hansíková
Keyword(s):  
Cytochromes P450 ◽  
Kinetic Studies ◽  
The Other ◽  
Maximal Velocity ◽  
Michaelis Constant ◽  
Other Hand ◽  
Plant Peroxidases ◽  
Tulip Bulbs

Tulip bulbs (Tulipa fosteriana, L.) contain peroxidases catalyzing the oxidation of the xenobiotics N-nitrosodimethylamine (NDMA) and N-nitroso-N-methylaniline (NMA). Three anionic (A1, A2, A3) and four cationic (B, C, D, E) peroxidases were purified from this tissue, partially characterized and used for kinetic studies. Demethylation of NDMA and NMA producing formaldehyde is catalyzed by one anionic (A1) and three cationic (C, D, E) peroxidases. The oxidation of NDMA by tulip peroxidases exhibits the Michaelis-Menten kinetics. The apparent Michaelis constant and the maximal velocity values for this substrate were determined. On the other hand, non-Michaelian kinetics for the NMA oxidation were observed with tulip peroxidases. The most abundant cationic peroxidase (peroxidase C) was used for detailed enzymatic studies. In addition to formation of formaldehyde, methylaniline, aniline, 4-aminophenol and phenol were found to be metabolites formed from NMA. Phenol was formed presumably by N-demethylation via a benzenediazonium ion, while methylaniline, aniline and 4-aminophenol were products of denitrosation of the substrate. The efficiencies of plant peroxidases to oxidize NDMA and NMA in vitro are compared with those of cytochromes P450 and discussed.

Responses of lactating ewes, offered fresh herbage indoors and when grazing, to supplements containing differing protein concentrations

1988 ◽  
Vol 46 (3) ◽  
pp. 403-415 ◽  
Author(s):  
P. D. Penning ◽  
R. J. Orr ◽  
T. T. Treacher
Keyword(s):  
Body Condition ◽  
Protein Concentration ◽  
Milk Protein ◽  
Fish Meal ◽  
Soya Bean ◽  
Protein Supplements ◽  
Bean Meal ◽  
Soya Bean Meal ◽  
Lamb Growth ◽  
Daily Milk

ABSTRACTThe responses to supplements differing in protein concentration and degradability were measured in lactating ewes and their twin lambs when offered fresh ryegrass either cut or grazed. Housed Scottish Halfbred ewes, offered fresh-cut grass ad libitum received no supplement (N) or supplements with barley and maize starch (B); barley and soya-bean meal (S); barley, soya-bean meal and fish meal (SF) or barley and fish meal (F) in weeks 2 to 7 of lactation. By feeding supplements, herbage organic-matter (OM) intake was depressed (2·00 v. 1·74 kg/day). Mean daily milk yield was increased when protein supplements were given and, because milk protein concentration was higher for supplement F and similar for all other diets, mean daily milk protein output increased with increasing fish meal in the diet. Milk yields were N 2·55, B 2·59, S 3·17, SF 3·15 and F 3·17 kg/day. Total milk solids and fat concentrations were also higher for S, SF and F than N or B. Lambs from ewes supplemented with protein grew faster and the ewes generally lost less weight and body condition compared with unsupplemented ewes.At pasture, Masham ewes grazed at herbage allowances of either 4 (L) or 10 (H) kg OM per day and received no supplement (N) or supplements B or F, for the first 6 weeks of lactation and then, in weeks 7 to 12, grazed without supplements. For NL, BL, FL, NH, BH and FH respectively lamb growth rates from birth to 6 weeks were 235, 242, 274, 267, 286 and 302 g/day; from birth to 12 weeks were 210, 209, 249, 255, 275 and 287 g/day and losses in ewe body-condition score from birth to 12 weeks were 1·28, 1·22, 1·06, 0·97, 0·62 and 0·76.It is concluded that protein supplements increased milk yield and lamb growth rates and that the response tended to be greater with fish meal.

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