scholarly journals The effect of different amino acid side chains on the stereospecificity and catalytic efficiency of the tryptophan synthase-catalysed exchange of the α-protons of amino acids

1996 ◽  
Vol 314 (3) ◽  
pp. 787-791 ◽  
Author(s):  
John J. MILNE ◽  
J. Paul G. MALTHOUSE
Keyword(s):  
Exchange Rate ◽  
Amino Acid ◽  
Exchange Rates ◽  
Catalytic Efficiency ◽  
Second Order ◽  
Tryptophan Synthase ◽  
Exchange Reactions ◽  
First Order ◽  
Allosteric Effector ◽  
Hydrogen Deuterium

1H-NMR has been used to follow the tryptophan synthase (EC 4.2.1.20) catalysed hydrogen–deuterium exchange of the α-protons of L- and D-alanine and -tryptophan. The first-order and second-order rate constants for exchange have been determined at pH 7.8 in the presence and absence of the allosteric effector, DL-α-glycerol 3-phosphate. In the presence of DL-α-glycerol 3-phosphate the stereospecificity of the tryptophan synthase-catalysed first-order exchange rates was in the order tryptophan > alanine > glycine. This increase in stereospecificity was largely due to the decrease in the magnitude of the first-order exchange rate of the slowly exchanged α-proton. A similar increase in the stereospecificity of the second-order exchange rates for alanine was also largely due to the decrease in the magnitude of the first-order exchange rate of the slowly exchanged α-proton of D-alanine. Adding DL-α-glycerol 3-phosphate produced an increase in the stereospecificity of the second-order exchange rate observed with alanine but no significant change in the stereospecificity of the first-order exchange rate with tryptophan. The α-subunits are shown to increase the exchange rates of the α-protons of L-alanine and L-tryptophan. We conclude that the contribution of the R-group of an amino acid to the stereospecificity of the exchange reactions of its α-proton can be similar to or larger than that of its α-carboxylate group. Possible mechanisms that could explain the stereospecificity of these exchange reactions are discussed.

scholarly journals The stereospecificity and catalytic efficiency of the tryptophan synthase-catalysed exchange of the α-protons of amino acids

2004 ◽  
Vol 381 (3) ◽  
pp. 847-852 ◽  
Author(s):  
Máire E. NíBEILLIÚ ◽  
J. Paul G. MALTHOUSE
Keyword(s):  
Amino Acids ◽  
Exchange Rates ◽  
Catalytic Efficiency ◽  
Deuterium Exchange ◽  
Proton Exchange ◽  
Tryptophan Synthase ◽  
Hydrogen Deuterium Exchange ◽  
Pka Values ◽  
First Order ◽  
Hydrogen Deuterium

13C-NMR has been used to follow the tryptophan synthase (EC 4.2.1.20) catalysed hydrogen–deuterium exchange of the pro-2R and pro-2S protons of [2-13C]glycine at pH 7.8. 1H-NMR has also been used to follow the tryptophan-synthase-catalysed hydrogen–deuterium exchange of the α-protons of a range of L- and D-amino acids at pH 7.8. The pKa values of the α-protons of these amino acids have been estimated and we have determined whether or not their exchange rates can be predicted from their pKa values. With the exception of tryptophan and norleucine, the stereospecificities of the first-order α-proton exchange rates are independent of the size and electronegativity of the amino acid R-group. Similar results are obtained with the second-order α-proton exchange rates, except that both L-tryptophan and L-serine have much higher stereospecificities than all the other amino acids studied.

scholarly journals Factors affecting the stereospecificity and catalytic efficiency of the tryptophan synthase-catalysed exchange of the pro-2R and pro-2S protons of glycine

1995 ◽  
Vol 311 (3) ◽  
pp. 1015-1019 ◽  
Author(s):  
J J Milne ◽  
J P G Malthouse
Keyword(s):  
Exchange Reaction ◽  
Catalytic Efficiency ◽  
Second Order ◽  
Beta Subunits ◽  
Enzyme Complex ◽  
Tryptophan Synthase ◽  
Exchange Reactions ◽  
Factors Affecting ◽  
Alpha Subunits ◽  
Beta 2

13C-NMR has been used to follow the tryptophan synthase (EC 4.2.1.20)-catalysed hydrogen-deuterium exchange of the pro-2R and pro-2S protons of [2-13C]glycine. The first- and second-order rate constants for exchange when the alpha 2 beta 2 enzyme complex is or is not saturated with glycine have been determined at pH 7.0 and 7.8. At pH 7.8 the effects of binding the allosteric effector, DL-alpha-glycerol 3-phosphate, and of removing the alpha-subunits have been examined. The beta-subunits preferentially catalyse the exchange of the pro-2R proton of glycine, but adding alpha-subunits decreases the stereospecificity of the exchange reactions. Likewise, binding of DL-alpha-glycerol 3-phosphate to the alpha 2 beta 2 enzyme complex causes a further decrease in the stereospecificity of this reaction. The stereospecificity of the second-order exchange reaction catalysed by the beta-subunits is 136-fold larger than that of the alpha 2 beta 2 enzyme complex in the presence of DL-alpha-glycerol 3-phosphate, while there is only a 5-fold decrease in the stereospecificity of the first-order exchange reaction under the same conditions. We discuss how these results relate to current theories which attempt to explain how the alpha-subunits and DL-alpha-glycerol 3-phosphate modify the catalytic properties of tryptophan synthase.

EXCHANGE REACTIONS OF IODIDE ION WITH AROMATIC IODIDES

1951 ◽  
Vol 29 (2) ◽  
pp. 154-161 ◽  
Author(s):  
A. M. Kristjanson ◽  
C. A. Winkler
Keyword(s):  
Activation Energies ◽  
Second Order ◽  
Exchange Reactions ◽  
First Order ◽  
Temperature Range ◽  
Iodide Ion

The exchange reactions of iodide ion with o- and p-nitroiodobenzene in the temperature range about 170°–238°C were apparently second order with activation energies of approximately 29 and 33.5 kcal. per mole respectively. In the same temperature range the exchange of iodide ion with iodobenzene and m-nitroiodobenzene appeared to be first order reactions, with activation energies of approximately 25 kcal. per mole.

Hydrogen—Deuterium Exchange in Bovine Serum Albumin Protein Monitored by Fourier Transform Infrared Spectroscopy, Part II: Kinetic Studies

2005 ◽  
Vol 59 (11) ◽  
pp. 1357-1364 ◽  
Author(s):  
Jože Grdadolnik ◽  
Yves Maréchal
Keyword(s):  
Exchange Rate ◽  
Exchange Rates ◽  
Kinetic Studies ◽  
Intensity Change ◽  
Water Molecules ◽  
Protein Backbone ◽  
Entire Interval ◽  
Stretching Vibration ◽  
Hydrogen Deuterium ◽  
Bending Modes

The set of infrared spectra recorded at different levels of hydrogen–deuterium (H/D) exchange as a function of time were processed using spectral decomposition. The most precise information about H/D exchange of the NH groups of the protein backbone was retrieved by observing the intensity change of the nearest C=O stretching vibration. The H/D exchange at the protein backbone begins with NH groups bonded to C=O with a characteristic frequency of 1683 cm−1. These amide groups were initially free and are the first to accept H-bonds from water during the hydration process. The NH groups, which are connected to C=O groups with a characteristic band at 1657 cm−1, exchange at a slower rate. For both populations the pairs of comparable exchange rates were calculated with rate constants of 10−3 min 1, 0.014 min 1, 0.0046 min 1, and 0.09 min 1. The appearance of two different exchange rates for each population is a consequence of the distinct exposure of particular molecular groups to the solvent. Two additional bands sensitive to exchange are attributed to NH bending modes in the side chains and are located at 1610 cm−1 and 1585 cm−1. These NH groups undergo H/D exchange at the beginning of the exchange with exchange rates of 0.019 min−1 and 0.17 min−1, respectively. The calculated exchange rate for hydrating water molecules is 0.037 min−1. The distribution of water's exchange rate is extremely broad and covers almost the entire interval of the time-dependent experiment. From the efficiency of the exchange (96%) it is evident that some parts of the protein are completely forbidden to water molecules.

Ligand exchange reactions of vanadium(III) β diketonate complexes

1978 ◽  
Vol 56 (7) ◽  
pp. 1012-1015 ◽  
Author(s):  
A. J. C. Nixon ◽  
D. R. Eaton
Keyword(s):  
Ligand Exchange ◽  
Zero Order ◽  
Second Order ◽  
Exchange Reactions ◽  
Rate Law ◽  
First Order ◽  
Kinetics Of ◽  
Incoming Ligand

The kinetics of ligand exchange reactions of V(III) β diketonates have been studied. The replacement of acetylacetone by hexafluoroacetylacetone involves a rate law with both first- and second-order terms in the incoming ligand. The replacement of acetylacetone by deuteroacetyl-acetone involves terms zero-order and first-order in the incoming ligand. Both reactions are markedly catalyzed by acids and inhibited by bases. A mechanism involving a dangling ligand intermediate is suggested. The rates of ligand exchange are much less than the rates of isomerization.

Nonlinear Analysis of Visual Evoked Potentials Elicited by Color Stimulation

1997 ◽  
Vol 36 (04/05) ◽  
pp. 315-318 ◽  
Author(s):  
K. Momose ◽  
K. Komiya ◽  
A. Uchiyama
Keyword(s):  
Visual System ◽  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Normal Subjects ◽  
Second Order ◽  
First Order ◽  
The Relationship ◽  
Perceived Color ◽  
Second Order Nonlinearity ◽  
Visual Evoked

Abstract:The relationship between chromatically modulated stimuli and visual evoked potentials (VEPs) was considered. VEPs of normal subjects elicited by chromatically modulated stimuli were measured under several color adaptations, and their binary kernels were estimated. Up to the second-order, binary kernels obtained from VEPs were so characteristic that the VEP-chromatic modulation system showed second-order nonlinearity. First-order binary kernels depended on the color of the stimulus and adaptation, whereas second-order kernels showed almost no difference. This result indicates that the waveforms of first-order binary kernels reflect perceived color (hue). This supports the suggestion that kernels of VEPs include color responses, and could be used as a probe with which to examine the color visual system.

Fear of Free Floating or Forced Exchange Rate Fixing

2004 ◽  
pp. 112-122
Author(s):  
O. Osipova
Keyword(s):  
Exchange Rate ◽  
Financial Crisis ◽  
Exchange Rates ◽  
Inflation Targeting ◽  
Exchange Rate Policy ◽  
Float Exchange Rate ◽  
Floating Exchange Rate ◽  
Rate Policy ◽  
Exchange Rate Arrangements ◽  
Pass Through

After the financial crisis at the end of the 1990 s many countries rejected fixed exchange rate policy. However actually they failed to proceed to announced "independent float" exchange rate arrangement. This might be due to the "fear of floating" or an irreversible result of inflation targeting central bank policy. In the article advantages and drawbacks of fixed and floating exchange rate arrangements are systematized. Features of new returning to exchange rates stabilization and possible risks of such policy for Russia are considered. Special attention is paid to the issue of choice of a "target" currency composite which can minimize external inflation pass-through.

Imaginings

2017 ◽  
Vol 9 (3) ◽  
pp. 17-30
Author(s):  
Kelly James Clark
Keyword(s):  
Religious Tradition ◽  
Second Order ◽  
Fine Tuning ◽  
Intellectual Humility ◽  
First Order ◽  
Natural Processes ◽  
Empirically Supported ◽  
Group Violence ◽  
The World ◽  
The Universe

In Branden Thornhill-Miller and Peter Millican’s challenging and provocative essay, we hear a considerably longer, more scholarly and less melodic rendition of John Lennon’s catchy tune—without religion, or at least without first-order supernaturalisms (the kinds of religion we find in the world), there’d be significantly less intra-group violence. First-order supernaturalist beliefs, as defined by Thornhill-Miller and Peter Millican (hereafter M&M), are “beliefs that claim unique authority for some particular religious tradition in preference to all others” (3). According to M&M, first-order supernaturalist beliefs are exclusivist, dogmatic, empirically unsupported, and irrational. Moreover, again according to M&M, we have perfectly natural explanations of the causes that underlie such beliefs (they seem to conceive of such natural explanations as debunking explanations). They then make a case for second-order supernaturalism, “which maintains that the universe in general, and the religious sensitivities of humanity in particular, have been formed by supernatural powers working through natural processes” (3). Second-order supernaturalism is a kind of theism, more closely akin to deism than, say, Christianity or Buddhism. It is, as such, universal (according to contemporary psychology of religion), empirically supported (according to philosophy in the form of the Fine-Tuning Argument), and beneficial (and so justified pragmatically). With respect to its pragmatic value, second-order supernaturalism, according to M&M, gets the good(s) of religion (cooperation, trust, etc) without its bad(s) (conflict and violence). Second-order supernaturalism is thus rational (and possibly true) and inconducive to violence. In this paper, I will examine just one small but important part of M&M’s argument: the claim that (first-order) religion is a primary motivator of violence and that its elimination would eliminate or curtail a great deal of violence in the world. Imagine, they say, no religion, too.Janusz Salamon offers a friendly extension or clarification of M&M’s second-order theism, one that I think, with emendations, has promise. He argues that the core of first-order religions, the belief that Ultimate Reality is the Ultimate Good (agatheism), is rational (agreeing that their particular claims are not) and, if widely conceded and endorsed by adherents of first-order religions, would reduce conflict in the world.While I favor the virtue of intellectual humility endorsed in both papers, I will argue contra M&M that (a) belief in first-order religion is not a primary motivator of conflict and violence (and so eliminating first-order religion won’t reduce violence). Second, partly contra Salamon, who I think is half right (but not half wrong), I will argue that (b) the religious resources for compassion can and should come from within both the particular (often exclusivist) and the universal (agatheistic) aspects of religious beliefs. Finally, I will argue that (c) both are guilty, as I am, of the philosopher’s obsession with belief. 

ANALISIS EKSPOSUR EKONOMI DAN FAKTOR-FAKTOR YANG MEMPENGARUHINYA PADA PERUSAHAAN ROKOK YANG TERCATAT DI BEI

Wahana ◽  
2019 ◽  
Vol 21 (2) ◽  
pp. 98-109
Author(s):  
Ida Musdafia Ibrahim ◽  
Arif Haryono
Keyword(s):  
Exchange Rate ◽  
Exchange Rates ◽  
Cash Flow ◽  
Firm Value ◽  
Tobacco Industry ◽  
Cash Flows ◽  
Least Square ◽  
Exchange Rate Risk ◽  
Positive Effects ◽  
Rate Risk

This study aims to analyze economic exposures and its factors namely exchange rates and inflation, that influence firm value as reflected through firm cash flow. Analytical method used Ordinary Least Square and eviews as analytical tool. This study used secondary data and cigarette industry companies listed on the Indonesia Stock Exchange as samples along 2008 to 2017. Samples choosing method used purposive sampling based on determined criterias. The results showed that partially economic exposure had positive effects on firm value but insignificant. These could be seen from the economic exposure factors influncenced namely exchange rates and inflations.The exchange rate risk has low influenced cash flow was caused of the tobacco industry has low level of export/import.Enhance,inflation also had low effect on cash flow was caused of the tendency of cigarette consumers will continue to buy cigarettes even though its price increases. In short, economic exposure in the tobacco industry has low influence toward firms value. Hence, simultaneously changes in exchange rates and inflation which are economic exposure indicators have a significant effect on cash flows.  Keywords: Economic Exposure, Exchange Rate Risk, Inflation Risk, Firms Value, Cash Flow

Exchange Rates as Exchange Rate Common Factors

2012 ◽  
Author(s):  
Ryan Greenaway ◽  
Nelson C. Mark ◽  
Donggyu Sul ◽  
Jyh-Lin Wu
Keyword(s):  
Exchange Rate ◽  
Exchange Rates ◽  
Common Factors
Sign in / Sign up

Export Citation Format

Share Document