Kinetic Consequences Research Articles

The chemical basis for interfacial activation of monomeric phospholipases A2. Autocatalytic derivatization of the enzyme by acyl transfer from substrate.

A basic monomeric phospholipase A2 from the venom of the American water moccasin, Agkistrodon piscivorus piscivorus, undergoes Ca2+-dependent, autocatalytic acylation during the course of hydrolysis of both model and natural phospholipid substrates. Acylation occurs at 2 lysine residues, Lys-7 and Lys-10, in the NH2-terminal alpha-helical segment of the enzyme, and when both positions are fully derivatized, the stable bisacylphospholipase A2 becomes a dimer in solution. The acylated enzyme is fully activated toward monomolecular layers of lecithins. Similar studies applied to the monomeric phospholipases A2 from porcine pancreas and from the venom of Agkistrodon contortrix contortrix also showed irreversible activation of the enzymes by substrate with the same kinetic consequences and formation of dimers. Acylation thus enables these enzymes to overcome the lag period observed under such conditions with native monomeric phospholipases, a phenomenon referred to as interfacial activation. Activation of the enzyme by acylation potentiates the phospholipase for interfacial recognition via formation of a dimeric enzyme. The naturally occurring phospholipase A2 dimer from Crotalus atrox venom displays no lag in the hydrolysis of lecithin monolayers nor does it undergo substrate level acylation. These facts support our proposal that dimerization concomitant with acylation is responsible for the large rate enhancements seen in the hydrolysis of aggregated phospholipids by monomeric phospholipases. Our findings demonstrate for the first time a chemical mechanism for interfacial activation of and interfacial recognition by phospholipases A2.

Thermodynamic and kinetic consequences of isomeric interplay

This paper surveys situations where observational or theoretical means have discovered the presence of several isomeric structures in an equilibrium. The effects of this isomerism on the evaluation of thermodynamic (and also partly kinetic) quantities are studied. Particular attention is given to the coexistence of two (or more) isomeric structures of comparable stability. The convolutional and deconvolutional treatments described are important for the interpretation of the overall observed terms, the prediction of properties and the behaviour of complex mixtures as well as for theory-experiment comparisons.

ATP-stimulated hydrolysis of GTP by RecA protein: kinetic consequences of cooperative RecA protein-ATP interactions.

The cooperativity of the single-stranded DNA dependent nucleoside triphosphatase activity of the recA protein was investigated by examining the influence of a good substrate (ATP) on the hydrolysis of a poor substrate (GTP). At pH 7.5 and 37 degrees C, both ATP and GTP are hydrolyzed with a turnover number of 17.5 min-1. The S0.5 for GTP (750 microM), however, is nearly 20-fold higher than the S0.5 for ATP (45 microM). Low concentrations of ATP activate the GTPase activity of the recA protein by lowering the S0.5 for GTP; in the presence of 50 microM ATP, the S0.5 for GTP is reduced from 750 microM to 200 microM. Concentrations of ATP greater than 50 microM result in competitive inhibition of the ATP-activated GTPase activity. Although GTP is a substrate for hydrolysis, it will not substitute for ATP as a high-energy cofactor in the standard recA protein promoted three-strand exchange reaction. To account for these results, a minimal kinetic model is presented in which ATP binding induces specific conformational changes in the recA protein that do not occur with GTP binding.

A comparative analysis of the synergistic interaction between N1-phenylsulfanilamides and benzylpyrimidines using qsar techniques.

Growth inhibition of E. coli cell culture has been determined for a series of 4-substituted-N1-phenylsulfonilamides tested in the presence and absence of synergistic concentrations of trimethoprim. Quantitative structure-activity relationships, established by regression analysis, exhibit an identical dependence of bacterial growth inhibition on sulfonamide pKa irrespective of the presence or absence of trimethoprim. Examination of a small series of benzylpyrimidines in the presence or absence of 4-dimethylamino-N1-phenylsulfanilamide gave similar results. Since the presence of a synergistic agent affords no change in structure-activity relationships, it is concluded that no direct interaction between sulfonamides and benzylpyrimidines occurs and that the synergism observed is solely the result of the kinetic consequences of sequential blockade of the folate biosynthetic pathway.

Control of the generation and reactions of free radicals in biological systems by kinetic and thermodynamic factors.

Quantifiable redox properties are useful predictors of substrate reactivity in enzyme-catalysed redox reactions of e.g. nitroreductases or peroxidases. Redox properties may also control the rates of electron-transfer reactions between radical products of reduction and oxidation, and endogenous oxidants and reductants respectively. However, in numerous instances prototropic properties of substrate or radical may have profound kinetic consequences, protonation of radicals frequently slowing down electron-transfer reactions. Further, reactions which are thermodynamically extremely unfavourable may still proceed if radical products are removed from the pre-equilibrium efficiently. Thus kinetic considerations often outweigh the purely thermodynamic viewpoint.

The mobile‐phase effects on stationary‐phase properties in capillary supercritical fluid chromatography

AbstractA significant uptake of supercritical mobile phases into immobilized stationary phases has been observed. The phase swelling effect has been evaluated hydrodynamically for SE‐30, SE‐54, and cyanopropyl silicone phases with respect to the mobile‐phase density of supercritical butane, column temperature, and the presence of a polar retention moderator. Some kinetic and retention consequences of the swelling phenomena are discussed.

The kinetic consequences of altering the catalytic residues of triosephosphate isomerase

The essential basic residue at the active site of the glycolytic enzyme triosephosphate isomerase is Glu-165, which is responsible for the abstraction of either the 1-pro-R proton of dihydroxyacetone phosphate or of the 2-proton of D-glyceraldehyde 3-phosphate, in the enolization steps that constitute the reaction catalysed by this enzyme. We have changed this residue to Asp by oligonucleotide-mediated site-directed mutagenesis, and have evaluated the free-energy profile for the mutant protein. Comparison of the detailed energetics of the wild-type and mutant enzymes shows that only the transition-state free energies have been seriously affected, each of the enolization steps having been slowed by a factor of about one thousand. Evidently the movement of a catalytic group by less than 1 Å (1 Å = 10 -1 nm = 10 -10 m) has dramatic effects on catalysis, and the nature of these effects can provide important information about enzyme mechanism and function.

Influence of smooth muscle myosin conformation on myosin light chain kinase binding and on phosphorylation

Conventional smooth muscle myosin preparations contain a tightly bound myosin light chain kinase activity, which is incompletely removed by gel filtration at high ionic strength. We show here that by contrast, this kinase activity is released, together with calmodulin, under conditions in which myosin is in the folded configuration. The conformation-related release of kinase occurred for dephosphorylated myosin in both the presence and absence of ATP and Ca 2+. Binding of kinase to extended phosphorylated myosin was relatively weaker than to dephosphorylated myosin, but was nonetheless detected. The kinetic consequences of this binding behaviour were determined by measuring initial myosin phosphorylation rates as a function of KCl concentration. Rate optima occurred at 60 mM KCl and 300 mM KCl, conditions favouring respectively stable filaments and stable extended monomers. Phosphorylation of the folded monomer was uniformly slow at low KCl concentrations. The folded moysin monomer is thus a relatively poor substrate for the kinase, and is therefore unlikely to represent an analog of the relaxed crossbridge configuration in myosin filaments.

Carbocation behavior in norbornyl-fused norbornyl systems. The kinetic and chemical consequences of fusing two norbornane units across framework bonds of various type

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCarbocation behavior in norbornyl-fused norbornyl systems. The kinetic and chemical consequences of fusing two norbornane units across framework bonds of various typeLeo A. Paquette, George DeLucca, Katsuo Ohkata, and Judith C. GallucciCite this: J. Am. Chem. Soc. 1985, 107, 4, 1015–1023Publication Date (Print):February 1, 1985Publication History Published online1 May 2002Published inissue 1 February 1985https://doi.org/10.1021/ja00290a044RIGHTS & PERMISSIONSArticle Views262Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Hydrolytic cleavage of p-nitrophenyl alkanoates in aqueous solutions of cyclodextrins

The hydrolytic cleavage of p-nitrophenyl alkanoates has been investigated in moderately alkaline aqueous solutions of α- and β-cyclodextrins. The catalytic effects of cyclodextrins (the kc/kun ratios) first decrease and then increase with increasing chain length. Such a trend is apparently related to the mode of insertion of the alkanoates into the cyclodextrin. Induced c.d. measurements indicate that only in the case of short-chain alkanoates (up to butyrate or hexanoate) the p-nitrophenyl moiety is included in the cyclodextrin cavity whereas for long-chain esters the hydrocarbon chain is inserted into it. The kinetic consequences of the dual mode of complexation and differences between the two types of cyclodextrins investigated are briefly discussed.

Role of hydrogen in pyrolysis of hydrocarbons.

Admixed H2 in the gas phase pyrolysis of olefins and aromatics was known to reduce the formation of higher boiling products. The background principles involved in the above have been reviewed. Kinetic consequences of the reaction have attributed to the following: it prevents the pyrolyzing system from accumulating resonance stabilized radicals such as allyl and benzyl and, thereby, establishes radical chain pyrolysis in which H-atom carries propagating chain. Rate determining step of the propagation cycle has been identified as comprising H-atom addition to C(sp2)-atom in the substrate molecule and spontaneous decomposition of the resulting chemically activated adduct radical. Changes in geometry and potential energy along the rate determining step have been discussed with special reference to a few selected cases. Selective cleavage of the bond adjacent to the electronegative site susceptible of H-atom attack has been suggested and exemplified by coal liquefaction induced by H-atom.

Oxygen-related thermal donors in silicon: A new structural and kinetic model

A structural model for the oxygen-related thermal donors produced at moderate temperatures (<500 °C) is presented, where electrical activity commences with clusters containing five or more oxygen atoms and arises from a silicon atom at the center of the cluster. The donor activity of a cluster is terminated upon the ejection of this central silicon atom in order to bring about stress relaxation. A large number of electrically active donor species are predicted, differing only in the number of oxygen atoms each species contains. This structural model satisfies the stringent symmetry requirements of electron paramagnetic resonance (EPR), explains the lack of hyperfine interaction with Si29 or O17 nuclei and the large multiplicity in the number of donor species observed by infrared spectroscopy and EPR. The proposed clusters are shown to be embryonic forms of the much larger rodlike defects examined in detail by electron microscopy. Chemical reaction theory is used to deduce the kinetic consequences of the structural model. Both approximate analytic and numerical solutions of the resulting coupled, nonlinear equations are presented. The numerical results provide a good description of the detailed infrared kinetic data on the growth of the individual donor species and, in addition, reproduce the well-known average kinetic data from resistivity measurements. In order to explain the dependence of the oxgyen diffusivity on the sample thermal history and the well-known diffusivity enhancement, a highly mobile oxygen-silicon interstitial complex is proposed, which provides a satisfactory description of the results of dichroic recovery experiments. It is shown, however, that the values of diffusivity deduced from donor formation studies are, in addition, strongly influenced by inhomogeneities in the oxygen distribution as well as by the presence of small, electrically inactive oxygen clusters prior to the anneal. It seems necessary to consider all these possibilities to explain the experimental data.

Allosteric regulatory properties of muscle phosphofructokinase.

We have reviewed the allosteric regulatory properties of skeletal muscle phosphofructokinase and recent results on the phosphorylation of this enzyme. The number and affinities of various ligand binding sites are described, and a simple three state model is presented to explain the kinetic and ligand-binding properties of the enzyme. Data describing a lack of fit to a concerted transition model are presented. The widespread occurrence of partial phosphorylation of phosphofructokinase at a specific site near the carboxyl terminus is documented, as well as the lack of significant kinetic consequences of such phosphorylation.

On the comparison of the theoretical and experimental data for the kinetics of the Cope rearrangement of 1,5-hexadiene

The Cope rearrangement of 1,5-hexadiene is treated as a process passing through an intermediate; this feature was verified by recent quantum-chemical studies. Relationships are derived between the characteristics of the both partial activation processes involved and the experimental data (which characterize the overall process). It is shown that proper consideration of the kinetic consequences of the existence of the intermediate might help to eliminate the recently reported large difference between the MINDO/3 activation entropy and the experimental entropy for the boat pathway for the Cope rearrangement.

Step heights associated with grain boundary dislocations in cubic crystals

The step vectors associated with perfect grain boundary dislocations in cubic crystals are determined for coincidence systems up to Σ37a. These determine the step heights which may be associated with the dislocations. Certain trends in the data are identified and rationalized : in particular, it is predicted that non-primitive grain boundary dislocations will be relatively stable in lower-coincidence boundaries. Structural and kinetic consequences of this prediction are discussed, and comparisons are drawn with available data.

The photocatalyzed oxidation of polyamides and polyolefins

Abstract

Activation and inactivation of acetylcholinesterase by metal ions.

The kinetic consequences of acetylcholinesterase peripheral site occupation by metal ions were examined using three substrates; acetylthiocholine, p-nitrophenylacetate, and 7-(dimethylcarbamoyloxy)-N-methylquinolinium iodide. Two classes of metal ion effects were noted: activation by a group including Mg2+, Ca2+, Mn2+, and Na+, and inactivation by a second group which to date includes Zn2+, Cd2+, Hg2+, Ni2+, Cu2+, and Pb2+. Activation is demonstrable only in solutions of low ionic strength whereas inactivation can be readily observed in solutions of both low and high ionic strength. Activation appears to be due to a combination of metal ion binding and ionic strength effects and involves binding to peripheral sites which are distinct from those which bind organic cationic activators such as gallamine, propidium, and 7-(dimethylcarbamoyloxy)-N-methylquinolinium. The principal activating effect is on the deacylation phase of the enzyme-substrate reaction. Inactivators effect a slow conversion of the enzyme to an unreactive form. The kinetics of inactivation are biphasic at low ionic strength but become essentially monophasic at high ionic strength. More than 80% of the enzyme activity can be recovered upon addition of EDTA provided the chelating agent is added immediately following completion of the inactivation process. Prolonged exposure to inactivators results in a progressive decrease in the amount of recoverable activity, Although peripheral ligand interactions may result in a variety of catalytic site conformations, the macroscopic properties can be accounted for in terms of three ligand-dependent states of the enzyme in which catalytic ability (actual or potential) is retained, and a fourth denatured state.

Thermodynamic and kinetic consequences of substitutional order/disorder in minerals

Thermodynamic and kinetic consequences of substitutional order/disorder in minerals

Kinetic analysis of simultaneously occurring proton-sorbose symport and passive sorbose transport in Saccharomyces fragilis

Sorbose transport in Saccharomyces fragilis takes place both via an active sugar-H + symport system and via facilitated diffusion. To establish whether the two modes of transport proceed via the same transporter or via two different carriers, the kinetic consequences of both models were investigated. The kinetic equations for initial transport were derived for three possible reaction sequences with respect to sugar and H + binding to the symport carrier: random binding and obligatory ordered binding with either sugar or H + binding first, yielding six sets of kinetic parameters. Analysis of experimental data of sorbose transport in S. fragilis showed the existence of separate carriers for active, sorbose-H + symport and facilitated diffusion. Furthermore, it could be concluded that the symport carrier shows random binding of sugar and H +. In recent literature, a similar combination of active and passive sugar transport in Rhodotorula gracilis and Chlorella vulgaris was interpreted as two modes of action of the same carrier, viz., active symport via the protonated, and facilitated diffusion via the unprotonated carrier. Analysis of the experimental data according to the criteria presented in this paper showed, however, that this supposition is untenable and that two different carriers must also be involved in these micro-organisms.

ChemInform Abstract: ELECTRON SPIN RESONANCE STUDY OF THE DECAY OF METHYL RADICAL‐BROMIDE ION PAIRS IN ACETONITRILE AT LOW TEMPERATURE

Methyl radicals adjacent to cyanide ions are generated upon photolysis of ..gamma..-irradiated, crystalline acetonitrile, and these radicals decay by hydrogen atom abstraction from neighboring matrix molecules. In this paper the kinetic consequences of a slight alteration in the immediate environment of the methyl radical are examined. It is found that replacement of the cyanide ion with a bromide ion causes the observed rate constant for abstraction to be lower by about a factor of 2 at low temperatures. Once again, the low activation energy and large deuterium kinetic isotope effect are indicative of very important tunnel effects in the abstraction reaction.