scholarly journals The significance of abrupt transitions in Lineweaver–Burk plots with particular reference to glutamate dehydrogenase. Negative and positive co-operativity in catalytic rate constants

1973 ◽  
Vol 131 (1) ◽  
pp. 97-105 ◽  
Author(s):  
Paul C. Engel ◽  
William Ferdinand
Keyword(s):  
Glutamate Dehydrogenase ◽  
Rate Equation ◽  
Rate Constants ◽  
Initial Rate ◽  
Current Knowledge ◽  
The Other ◽  
Catalytic Rate Constant ◽  
Catalytic Rate ◽  
Linear Sections ◽  
Glucose 6 Phosphate Dehydrogenase

1. Lineweaver–Burk plots for glutamate dehydrogenase, glucose 6-phosphate dehydrogenase and several other enzymes show one or more abrupt transitions between apparently linear sections. These transitions correspond to abrupt increases in the apparent Km and Vmax. with increasing concentration of the varied substrate. 2. The generalized reciprocal initial-rate equation for a multi-site enzyme requires several restrictions to be put on it in order to generate such plots. These mathematical conditions are explored. 3. It is shown that the effective omission of a term in the denominator of the reciprocal initial-rate equation represents a minimal requirement for generation of abrupt transitions. This corresponds in physical terms to negative co-operativity followed by positive co-operativity affecting the catalytic rate constant for the reaction. 4. Previous models for glutamate dehydrogenase cannot adequately account for the results. On the other hand, the model based on both negative and positive co-operativity gives a good fit to the experimental points. 5. The conclusions are discussed in relation to current knowledge of the structure and mechanism of glutamate dehydrogenase.

scholarly journals Sources of ammonia for mammalian urea synthesis

1978 ◽  
Vol 176 (3) ◽  
pp. 733-737 ◽  
Author(s):  
H A Krebs ◽  
R Hems ◽  
P Lund ◽  
D Halliday ◽  
W W Read
Keyword(s):  
Glutamate Dehydrogenase ◽  
Initial Rate ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
The Other ◽  
Amino Group ◽  
Urea Synthesis ◽  
Purine Nucleotide ◽  
Carbamoyl Phosphate ◽  
Purine Nucleotide Cycle

The initial rate of incorporation of [15N]alanine into the 6-amino group of the adenine nucleotides in rat hepatocytes was about one-eighteenth of the rate of incorporation into urea. Thus the purine nucleotide cycle cannot provide most of the ammonia needed in urea synthesis for the carbamoyl phosphate synthase reaction (EC 2.7.2.5). On the other hand, contrary to the view expressed by McGivan & Chappell [(1975) FEBS Lett. 52, 1–7], the experiments support the view that hepatic glutamate dehydrogenase can supply the required ammonia.

The kinetics of the reactions of sheep haemoglobin with iso cyanides

1960 ◽  
Vol 152 (948) ◽  
pp. 331-345 ◽  
Keyword(s):  
Chain Length ◽  
Steric Hindrance ◽  
Rate Constants ◽  
Homologous Series ◽  
Experimental Error ◽  
Initial Rate ◽  
The Other ◽  
Tertiary Butyl ◽  
Kinetics Of ◽  
Haemoglobin Molecule

The kinetic basis for the decrease in affinity of haemoglobin and myoglobin for successive members of the series of alkyl iso cyanides has been investigated. The initial rate of combination of ethyl, n -propyl, iso propyl, iso butyl and tertiary butyl iso cyanides with haemoglobin and with myoglobin decreases with increasing chain-length by about 500-fold in the case of haemoglobin and about 40-fold in the case of myoglobin. The rate of combination of the fourth iso cyanide molecule with haemoglobin (i. e. I + Hb 4 I 3 → Hb 4 I 4 ) is, however, only about 14 times smaller for tertiary butyl as compared with ethyl iso­ cyanide; this finding is in line with Pauling’s suggestion that combination of successive ligand molecules with haemoglobin decreases the steric hindrance for combination with further ligand molecules. The latter effect, however, varies considerably from ligand to ligand and is not only a property of the haemoglobin molecule. The velocity of dissociation of the first molecule of iso cyanide from saturated haemoglobin, on the other hand, is the same within experimental error for all members of the series. With myoglobin the rate constants for dissociation show differences of two- to three-fold, but there is no systematic trend. Thus the burden of accounting for the differences in affinity between the iso cyanides falls upon the combination velocity constants. This finding is in contrast to that for the gaseous ligands O 2 , CO and NO, where the affinity is primarily determined by the dissociation velocity constants. The bearing of the results on the ‘crevice’ hypothesis of haemoglobin structure is discussed. In line with the well-known fact that the first member of an homologous series is often anomalous it was found that the rate of dissociation of methyl iso cyanide from haemoglobin was about 50 times greater than that for all the higher homologues of the series. Preliminary experiments were carried out on the rate of combination of free haem with several of the iso cyanides, but were not pursued further on account of the difficulties mentioned in the text.

The pseudomalachite-ludjibaite-reichenbachite conundrum: OD description

2019 ◽  
Vol 57 (5) ◽  
pp. 571-581
Author(s):  
Emil Makovicky
Keyword(s):  
Crystal Structures ◽  
Current Knowledge ◽  
The Other ◽  
Crystal Chemical ◽  
Layer System ◽  
Coordination Polyhedra

Abstract Crystal structures of the three polymorphs of Cu5(PO4)2(OH)4, namely pseudomalachite, ludjibaite, and reichenbachite, can be described as being composed of rods perpendicular to their crystal-chemical layering. Two different sorts of rods can be defined. Type 1 rods share rows of Cu coordination polyhedra, forming a series of slabs. Slab boundaries and slab interiors represent alternating geometric OD layers of two kinds, with layer symmetries close to P21/m and , which make up two different stacking schemes of geometric OD layers in the structures of ludjibaite and pseudomalachite. Such OD layers, however, are not developed in reichenbachite. Type 2 rods are defined as having columns of PO4 tetrahedra in the corners of the rods. In the Type 2 slabs composed of these rods, geometric Pg OD layers of glide-arrayed tetrahedra alternate with more complex OD layers; in ludjibaite this system of layers is oriented diagonally with respect to the Type 1 OD layer system. Two different OD stackings of Type 2 OD layers form the ludjibaite and reichenbachite structures but not that of pseudomalachite. Thus, ludjibaite might form disordered intergrowths with either of the other two members of the triplet but reichenbachite and pseudomalachite should not form oriented intergrowths. Current knowledge concerning formation of the three polymorphs is considered.

Solvolysis kinetics and mechanism of substituted 3-acetyl-1,3-diphenyltriazenes in acid medium; Kinetic acidity function

1987 ◽  
Vol 52 (9) ◽  
pp. 2212-2216
Author(s):  
Oldřich Pytela ◽  
Martin Kaska ◽  
Miroslav Ludwig ◽  
Miroslav Večeřa
Keyword(s):  
Acid Medium ◽  
Sulphuric Acid ◽  
Rate Constants ◽  
Decomposition Kinetics ◽  
Acidity Function ◽  
Hammett Equation ◽  
Kinetic Acidity ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Catalytic Rate

The decomposition kinetics has been measured of fourteen 3-acetyl-1,3-bis(subst. phenyl)triazenes in 40% (v/v) ethanol and sulphuric acid. The kinetic acidity function and catalytic rate constants have been determined from the rate constants observed. Mechanism has been suggested for the general acid-catalyzed solvolysis from comparison of the course of the kinetic acidity function and H0 function and from the reaction constant of the Hammett equation.

PLATELET AGGREGATION DOES NOT CONFORM TO SIMPLE PARTICLE COLLISION THEORY

1987 ◽  
Author(s):  
Moideen P Jamaluddin
Keyword(s):  
Platelet Aggregation ◽  
Rate Equation ◽  
Rate Constants ◽  
Kinetic Scheme ◽  
Order Type ◽  
Second Order ◽  
Particle Collision ◽  
Collision Theory ◽  
Rate Law ◽  
First Order

Platelet aggregation kinetics, according to the particle collision theory, generally assumed to apply, ought to conform to a second order type of rate law. But published data on the time-course of ADP-induced single platelet recruitment into aggregates were found not to do so and to lead to abnormal second order rate constants much larger than even their theoretical upper bounds. The data were, instead, found to fit a first order type of rate law rather well with rate constants in the range of 0.04 - 0.27 s-1. These results were confirmed in our laboratory employing gelfiltered calf platelets. Thus a mechanism much more complex than hithertofore recognized, is operative. The following kinetic scheme was formulated on the basis of information gleaned from the literature.where P is the nonaggregable, discoid platelet, A the agonist, P* an aggregable platelet form with membranous protrusions, and P** another aggregable platelet form with pseudopods. Taking into account the relative magnitudes of the k*s and assuming aggregation to be driven by hydrophobic interaction between complementary surfaces of P* and P** species, a rate equation was derived for aggregation. The kinetic scheme and the rate equation could account for the apparent first order rate law and other empirical observations in the literature.

Methylene. III. Gas phase reactions with 1-chloropropane

1969 ◽  
Vol 312 (1509) ◽  
pp. 141-161 ◽  
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Hydrogen Abstraction ◽  
The Other ◽  
Gas Phase Reactions ◽  
Other Hand ◽  
Chlorine Substituent ◽  
High Degree ◽  
Singlet Methylene

The work described in this and the following paper is a continuation of that in parts I and II, devoted to elucidation of the mechanism of the reactions of methylene with chloroalkanes, with particular reference to the reactivities of singlet and triplet methylene in abstraction and insertion processes. The products of the reaction between methylene, prepared by the photolysis of ketene, and 1-chloropropane have been identified and estimated and their dependence on reactant pressures, photolysing wavelength and presence of foreign gases (oxygen and carbon mon­oxide) has been investigated. Both insertion and abstraction mechanisms contribute significantly to the over-all reaction, insertion being relatively much more important than with chloroethane. This type of process appears to be confined to singlet methylene. If, as seems likely, there is no insertion into C—Cl bonds under our conditions (see part IV), insertion into C2—H and C3—H bonds occurs in statistical ratio, approximately. On the other hand, the chlorine substituent reduces the probability of insertion into C—H bonds in its vicinity. As in the chloroethane system, both species of methylene show a high degree of selectivity in their abstraction reactions. We find that k S Cl / k S H >7.7, k T Cl / k T H < 0.14, where the k ’s are rate constants for abstraction, and the super- and subscripts indicate the species of methylene and the type of atom abstracted, respectively. Triplet methylene is discriminating in hydrogen abstraction from 1-C 3 H 7 Cl, the overall rates for atoms attached to C1, C2, C3 being in the ratios 2.63:1:0.

THE ISOPIESTIC METHOD APPLIED TO SORPTION ISOTHERMS

1949 ◽  
Vol 27b (2) ◽  
pp. 87-100 ◽  
Author(s):  
S. Barnartt ◽  
J. B. Ferguson
Keyword(s):  
Carbon Tetrachloride ◽  
Linear Relation ◽  
Sorption Isotherms ◽  
Sorption Process ◽  
The Other ◽  
Isopiestic Method ◽  
Simple Criterion ◽  
Water Vapors ◽  
Linear Sections ◽  
Wide Pressure

The isopiestic method has been applied to the sorption of carbon tetrachloride and water vapors by activated coconut shell charcoals. The isopiestic charges were found to be linearly related over wide pressure ranges. Isotherms formed by plotting the isopiestic charges of two charcoals one against the other consisted of three linear sections for both carbon tetrachloride and water. If the pressure isotherm of one charcoal be known, those of other charcoals may be computed from it by weighing relatively few isopiestic charges. Errors inherent in the measurement of equilibrium pressures, as well as those caused by the drift of the pressure isotherms towards higher sorption capacities at a given pressure, are eliminated in the isopiestic method of comparing charcoals. The linear relation between the isopiestic charges affords a simple criterion of rejection for equations proposed to fit the pressure isotherms. It also throws into relief the structural regularities in activated charcoals. The existence of discontinuities m the sorption process, reported by previous experimenters, is supported by the isopiestic data.

Allosteric behaviour of 1:5 hybrids of mutant subunits of Clostridium symbiosum glutamate dehydrogenase differing in their amino acid specificity

2001 ◽  
Vol 360 (3) ◽  
pp. 651-656 ◽  
Author(s):  
Arun GOYAL ◽  
Xing-Guo WANG ◽  
Paul C. ENGEL
Keyword(s):  
Amino Acid ◽  
Glutamate Dehydrogenase ◽  
Cysteine Residue ◽  
The Other ◽  
Wild Type Enzyme ◽  
Triple Mutant ◽  
Subunit Stoichiometry ◽  
Clostridium Symbiosum ◽  
Mutant Forms ◽  
Fold Activation

Hybrid hexamers were made by refolding mixtures of two mutant forms of clostridial glutamate dehydrogenase. Mutant Cys320Ser (C320S) has a similar activity to the wild-type enzyme, but is unreactive with Ellman's reagent, 5,5′-dithiobis(2-nitrobenzoate) (DTNB). The triple mutant Lys89Leu/Ala163Gly/Ser380Ala (K89L/A163G/S380A), active with norleucine but not glutamate, is inactivated by DTNB, since the amino acid residue at position 320 is a cysteine residue. The chosen ratio favoured 1:5 hybrids of the triple mutant and C320S. The renatured mixture was treated with DTNB and separated on an NAD+–agarose column to which only C320S subunits bind tightly. Fractions were monitored for glutamate and norleucine activity and for releasable thionitrobenzoate to establish subunit stoichiometry. A fraction highly enriched in the 1:5 hybrid was identified. Homohexamers (C320S with 40mM glutamate and 1mM NAD+ at pH8.8, or K89L/A163G/S380A with 70mM norleucine and 1mM NAD+ at pH8.5) showed allosteric activation; succinate activated C320S approx. 50-fold (EC50 = 70mM, h = 2.4), and glutarate gave approx. 30-fold activation (EC50 = 35mM, h = 2.3). For the triple mutant, corresponding values were 80mM and 2.2 for succinate, and 75mM and 1.7 for glutarate, but maximal activation was only about 2-fold. In the 1:5 hybrid, with only one norleucine-active subunit per hexamer, responses to glutarate and succinate were still co-operative, and activation was more extensive than in the triple mutant homohexamer. A single norleucine-active subunit can thus respond co-operatively to a substrate analogue at the other five inactive sites. On the other hand, similar hyperbolic dependence on the norleucine concentration for the hybrid and the triple mutant homohexamer reflected the inability of C320S subunits to bind norleucine. With glutamate at pH8.8, an h value of 3.6 was obtained for the 1:5 hybrid, in contrast with an h value of 5.2 for the C320S homohexamer. The ‘foreign’ subunit evidently impedes inter-subunit communication to some extent.

Variant Plasminogens in Patients with a History of Venous Thrombosis

1979 ◽  
Author(s):  
K.C. Robbins ◽  
R.C. Wohl ◽  
L. Summaria
Keyword(s):  
Venous Thrombosis ◽  
Rate Constants ◽  
Autosomal Dominant ◽  
Binding Properties ◽  
Activation Data ◽  
History Of ◽  
Michaelis Constants ◽  
Catalytic Rate ◽  
Abnormal Plasminogen ◽  
Activation Rates

Kinetic methods will be described For measuring plasminogen and for studying plasminoge activation in human plasma, using specific synthetic substrates, with different activat, species. These studies resulted in the discovery of several patients plasmas containin-variant, or abnormal, plasminogen molecules; these plasmas showed lower observable activation rates. Plasminogen isolated from these plasmas activated with Identical catalytic rate constants to normal plasminogen, by different activator species, but the apparent Michaelis constants were 10- to 100-fold higher. These data lead to the conclsion that the binding properties of the activator species to the variant plasminogens have been impaired. The interpretation of the data In two patients with venous thrpto-sis was possible only in terms of homogeneous populations of plasminogen molecules. These individuals have to be considered homozygous with respect to their plasminogens, and Family studies Indicate the possibility of an autosomal dominant hereditary transmission. The urokinase activation data with the variant plasminogens point to an activation mechanisn identical to that proposed for streptokinase, namely the activation of Plasminogen hy a plasminogen-urokinase complex, analogous with the plasminogen-streptokinase comnlex.

Sign in / Sign up

Export Citation Format

Share Document