Ordinate Intercept Research Articles

Temperature influences on surface energetic parameters evaluated at solid–liquid interfaces

AbstractThe adhesive events experienced by a solid material upon contact with a biofluid are related to measurable surface properties of the solid; consequently, surface properties have been suggested to provide direction for the prediction and control of biofluid behavior at interfaces. With respect to biofilm formation at elevated temperatures, knowledge of temperature influences on such properties would serve to assist the development of predictive models that incorporate a surface‐related influence. In this work, surface energetic parameters for a variety of engineering materials were determined at temperatures of 7–80°C using contact angle analysis with a modified sessile drop technique. Specifically, a linear relationship between the polar component of the work of adhesion and the polar component of liquid surface tension, observed for each material, was characterized by its slope and intercept at each temperature. The value of the slope was observed to decrease linearly with temperature. The negative values of the ordinate intercept were observed to increase in magnitude with temperature for low‐energy surfaces, but did not change uniformly for solids of higher surface energy. The polar component of the work required to remove water from a surface, observed to decrease with decreasing polar character of a solid at a given temperature, was observed to decrease with increasing temperature. The observed temperature effects indicate a need to account for this influence in the development of models describing biofluid–contact surface interactions at temperatures outside of the ambient range.

Ventricular volume measurement from a multiplanar transesophageal ultrasonic imaging system: an in vitro study

We have developed a system to assess the feasibility of using multiple transesophageal ultrasonic images to measure left-ventricular volume, an important variable in patient management. The system includes a special transesophageal probe with a micromanipulator for acquiring cardiac images in multiple planes with known interplanar spatial relationship and an off-line processing system to compute the volume. In vitro studies with the probe demonstrated that the distance between two targets in space can be identified within 2 mm (SD = 0.4 mm) for points in the imaging plane 3.4 mm (SD = 0.5 mm) for points not lying in the imaging plane. This gives an average accuracy of +/- 6.5% for distances greater than 4.5 cm. Comparison of ultrasonic measurements of the volume of water-filled balloons and excised hearts to the volume required to fill them, revealed a correlation coefficient of 0.992, a regression line having a slope of 1.0 and an ordinate intercept at 0.2 mL, and a standard error of the estimate of 8 mL.

Evaluation of crosslinking and scission yields in irradiated polymers from the dose dependence of the weight- and z-average molecular weights

A procedure has been developed for the determination of scission and cross-linking fields, G(S) and G(X), in irradiated polymers by combination of the ordinate intercepts of plots of ([Mw(0)/ MW(D)] - 1)/D and ([Mz(0)/A/2(D)] - 1)/D versus dose (D). The required weight- and z-average molecular weight data for a given sample can be obtained by using the Rayleigh and schlieren optical systems, respectively, to record the solute distribution in a single sedimentation equilibrium experiment. The procedure has been tested by application to simulated data for a range of initial molecular weight distributions and values of G(S)/G(X) and applied to previous sedimentation equilibrium results (Nichol, J. M.; Donnell, J. H.; Rahman, NLP.; Winzor, D. J. J. Polym. Sci., Polym. Chem. Ed. 1977,15, 2919) for a polystyrene sample with Afw(0)/Mn(0) = 1.03 and G(S)/G(X) = 1.

Appendix to the sulfur-cyanolysis sites of serum albumin: metabolite competition studies. Tight-binding inhibitions that yield atypical Henderson plots.

Ordinary tight-binding inhibition in steady-state enzyme systems is conveniently evaluated by means of the Henderson plot. This is a linear plotting form that has an ordinate intercept equal to the total enzyme concentration. However, there are two experimental situations that yield deviations from the common Henderson plot form. These are inhibitor binding in a separate, noninhibitory mode that depletes the concentration of free inhibitor, and partial inhibition, i.e., the retention of partial activity by the enzyme-inhibitor complex. Noninhibitory depletion results in Henderson plots with elevated ordinate intercepts. Competitive partial inhibition yields a characteristic pattern of parabolic Henderson plots.

Kinetic and pharmacological properties of the GABA‐induced chloride current in Aplysia neurones: a ‘concentration clamp’ study

1. gamma-Aminobutyric acid (GABA) was applied by the 'concentration clamp' technique to isolated neurones of Aplysia. GABA induced a chloride current (ICl) due to activation of a single class of chloride-channel. 2. The concentration-response curve for the peak ICl gave an apparent dissociation constant of 6.4 X 10(-5) M and a Hill coefficient of 0.88. The current-voltage relationship was linear in the voltage range examined (-40 to +10 mV). 3. The activation phase of the ICl could be fitted to a single exponential function and desensitization followed the sum of two exponential functions. The time constants of activation and desensitization decreased with increasing concentrations of GABA but were voltage-independent. The recovery process from desensitization also followed the sum of two exponential functions. 4. As for the rate-limiting step of the channel activation, the hyperbolic relationship between the activation rate and GABA concentration showed that the rapid binding assumption holds, suggesting that the isomerization step is rate-limiting. The apparent channel closing rate constant was estimated to be 10 s-1 from the ordinate intercept of the linear part of the above relationship at lower concentrations. 5. Muscimol and beta-alanine induced a ICl, which cross-desensitized with that evoked by GABA. The GABA-ICl was not enhanced by diazepam (10(-6) M) or alpha-chloralose (10(-3) M), in fact depressant effects were evident. 6. Pentobarbitone decreased the GABA-ICl non-competitively without altering activation or desensitization kinetics. The concentration-inhibition curve gave a KD value of 8.9 x 10(-5) M and a Hill coefficient of 1.0. 7. These results suggest that GABA activates a single class of Cl channel in Aplysia neurones, which have one binding site for the agonist. The GABA receptor-Cl channel complex in Aplysia is pharmacologically and perhaps structurally different from that in vertebrates.

The barley protein degradation: Mechanism of protein solubilization during barley mashing with neutral proteinase

Kinetics of protein solubilization during barley mashing with neutral proteinase were studied. By plotting the kinetics data in Foster-Niemann coordinates for barley concentration range of 10-30% linear relationships with high correlation coefficients (r >/= 0. 999) were obtained. The slopes of straight lines were very close to corresponding reciprocal initial insoluble nitrogen concentrations. Barley proteolytic inhibitors affected the ordinate intercept; by their addition the values of ordinate intercept decreased. The data suggest that the modified Foster-Niemann equation can be proposed to interpret kinetics of insoluble barley protein degradation. The proteolytic activity decay was studied as well. The enzyme decay was faster in buffer solution than during barley mashing, but in both cases first-order kinetics can be applied. A mathematical model describing protein solubilization and enzyme decay kinetics were developed. The results of computer simulation were in good agreement with experimental data.

Plasma concentrations of noradrenaline and 3,4-dihydroxyphenylethyleneglycol under conditions of enhanced sympathetic activity.

Antecubital venous blood was sampled at rest and during orthostasis or supine bicycle exercise. The plasma was analyzed for noradrenaline and 3,4-dihydroxyphenylethyleneglycol (DOPEG) by HPLC. Orthostasis resulted in increases in plasma concentrations of both noradrenaline and DOPEG. The magnitude of changes in both was dependent on the degree of orthostasis. In conditions of supine rest, sitting, and standing the plot of the geometric mean values of plasma DOPEG (ordinate) against those of plasma noradrenaline was linear, had a slope of about unity, and intersected the ordinate at a finite value of plasma DOPEG. After administration of desipramine (to block uptake), plasma concentrations of DOPEG fell both at rest and during orthostasis. Moreover, desipramine abolished the plasma DOPEG response to orthostasis without affecting the plasma noradrenaline response. Hence, changes in plasma DOPEG brought about by changes in sympathetic tone are presynaptic in origin. The plasma concentration of DOPEG observed in the presence of desipramine was virtually identical with the ordinate intercept of the regression line relating plasma DOPEG to plasma noradrenaline in the absence of desipramine. This pool of plasma DOPEG (which amounted to about 75% of that observed at supine rest in the absence of desipramine) probably stems from intraneuronal noradrenaline leaking out of the storage vesicles of peripheral sympathetic neurones and may in part also be derived from the central nervous system. Supine bicycle exercise failed to increase plasma DOPEG. This may be due to the separation of the sampling site from the site of noradrenaline release (i.e. the exercising limbs) by organs involved in DOPEG extraction.(ABSTRACT TRUNCATED AT 250 WORDS)

The apparent Km is a misleading kinetic indicator.

When information concerning whether or not a ligand interacts with the same enzyme species as do the substrates, the variation of the Michaelis constant Km (for each substrate) with ligand concentration is sometimes used as a diagnostic. It is shown that the Michaelis constant is of no particular value in this respect and may be misleading. Thus, depending on the mechanism, Km may vary with ligand concentration even though the ligand interacts with species far removed in the mechanism from the substrate-binding steps, and it may stay constant in cases where the ligand competes directly for the free enzyme. In contrast, the slope of a double-reciprocal plot of the kinetic data (= Km/Vmax.) (or, equivalently, the ordinate intercept of a Hanes plot A/v versus A, where A is the substrate concentration) independently of the particular mechanism involved uniquely signifies whether or not such interaction occurs. The results clearly indicate that, for purposes other than communicating the substrate concentration yielding control of the enzymic activity, usage of Km and its variation with ligand concentration should be avoided and interest instead focused on the slope, in accordance with the long-established rules of Cleland [Biochim. Biophys. Acta (1963) 67, 188-196], for which the present analysis provides the formal framework.

The determination of specificity constants in enzyme-catalysed reactions.

A convenient and accurate procedure for determining the kinetic parameter Vmax./Km is described. This avoids the error in the usual method of taking the observed first-order rate constant of an enzymic reaction at low substrate concentration as Vmax./Km. A series of reactions is used in which the initial concentration of substrate is below Km (e.g. from 5% to 50% of Km). Measurements are taken over the same extent of reaction (e.g. 70%) for each member of the series, and treated as if the kinetics were truly first-order. The reciprocal of the observed first-order rate constant is then plotted against the initial concentration of substrate: the reciprocal of the ordinate intercept is Vmax./Km. The procedure, as well as being applicable to simple reactions, is shown to be valid when there is competitive inhibition by the product, or when the reaction is reversible, or when there is competitive or mixed inhibition. The hydrolysis of cephalosporin C by a beta-lactamase from Pseudomonas aeruginosa is used to illustrate the method.

Determination of membrane potential with lipophilic cations: correction of probe binding

The binding of lipophilic ions to the membrane of envelope vesicles from Halobacterium halobium was examined in the absence and presence of membrane potential. The lipophilic ions used constitute a homologous series of (Phe) 3-P +-(CH 2) n-CH 3 ( n = 0–4) and tetraphenylphosphonium (TPP +). In the absence of membrane potential, the amounts of binding were proportional to the probe concentration in the medium when the concentration is dilute. Upon illumination, interior negative membrane potential is generated which induces the uptake of phosphonium cation probe. 2 μM were employed as the initial probe concentration. The real membrane potential was evaluated by means of extrapolation to the state of no binding: The values of C i app C o for various probes are plotted against the binding coefficient. Here, C i app is the apparent intra-vesicular concentration of the probes which is calculated without consideration of bound probes. The ordinate intercept of the plot gives the true concentration ratio, and from this the membrane potential is evaluated. The membrane potential-dependent binding was analysed with a model: the membrane is split into two halves, outer and inner half, and the amounts of bound probes in each region are governed by the concentration in the contiguous solution. We obtained a formula which describes amounts of binding as a function of the membrane potential.

Oxidation of carbon monoxide on thin film catalysts: Characterization by a critical temperature measurement

Platinum catalyst thin films prepared by PtO 2 decomposition are tentatively characterized by the transition between two stationary reaction states both at constant temperature and constant CO partial pressure. It is demonstrated that at constant temperature, the measurements must be made in the sense of decreasing CO concentration because of reactant diffusion and heat dissipation. Following the model of R. Dagonnier, M. Dumont, and J. Nuyts ( J. Catal. 66, 130 (1980)), a sum of activation energies corresponding to the surface reaction and the dissociative oxygen adsorption was determined. This sum of activation energies and the ordinate axis intercepts of the Arrhenius plot presented are found to change with ageing of the samples.

Quasielastic light-scattering studies on dinucleosomal-sized DNA: ionic-strength dependence.

AbstractQuasielastic light‐scattering (QELS) studies were performed on a monodisperse preparation of dinucleosomal‐sized DNA having an average of 375 base pairs. The QELS data were obtained at several time intervals at each angle examined over the range 30° < θ < 60° for the ionic strength solvents 500, 50, 10, and 1 mM in KCl. What results from this study is that two relaxation domains persist over the entire ionic strength range where the “splitting” between these two domains increases as the ionic strength is lowered. The ordinate intercept of Dapp vs Cp/2Cs, where Cp is the polyion concentration and Cs is the added salt concentration, is shown to give the “true” hydrodynamic value for the diffusion coefficient. The “splitting phenomenon” is interpreted in terms of two models currently in vogue: small ion–polyion coupled modes and translational–rotational coupled modes for rigid rods in congested solutions. Although neither model is in perfect agreement with the experimental results, the small ion–polyion coupled mode theory appears to provide a better quantitative description of the observations.

THE BARLEY PROTEIN DEGRADATION: EFFECT OF NEUTRAL PROTEINASE CONCENTRATION ON PROTEIN DEGRADATION KINETICS

The time course of barley protein degradation was investigated in two cases: (i) in mashing of raw barley with different concentrations of bacterial neutral proteinase in the presence of α-amylase. and (ii) in mashing of spent grains, remaining after barley syrup preparation, with different proteinase concentrations. Protein solubilisation and α-amino nitrogen liberation rates decrease in the course of barley and spent grains hydrolysis. Initial protein degradation rates in spent grains mashing are lower than in native barley. Gel-chromatography of supernatants of the mash in the course of hydrolysis has indicated that the proteinase becomes increasingly occupied with solubilised proteins as the process proceeds. plotting the kinetics data for protein solubilisation in Foster-Niemann coordinates straight lines with high correlation (r=0·999) for both cases of hydrolysis have been obtained. For different enzyme concentrations the straight lines have been closely parallel with positive slope. A high correlation between ordinate intercept in Foster-Niemann coordinates and proteinase concentrations has been obtained. Linear correlations in Foster-Niemann coordinates for α-amino nitrogen liberation process have also been observed. However, for α-amino nitrogen liberation, the correlation between the ordinate intercept and proteinase concentration has not been achieved. The possibilities of application of kinetics parameters (ordinate intercept slope) as quantitative measures of enzyme efficiency in protein degradation under different conditions has been emphasised.

Graphical evaluation of blood-to-brain transfer constants from multiple-time uptake data.

A theoretical model of blood-brain exchange is developed and a procedure is derived that can be used for graphing multiple-time tissue uptake data and determining whether a unidirectional transfer process was dominant during part or all of the experimental period. If the graph indicates unidirectionality of uptake, then an influx constant (Ki) can be calculated. The model is general, assumes linear transfer kinetics, and consists of a blood-plasma compartment, a reversible tissue region with an arbitrary number of compartments, and one or more irreversible tissue regions. The solution of the equations for this model shows that a graph of the ratio of the total tissue solute concentration at the times of sampling to the plasma concentration at the respective times (Cp) versus the ratio of the arterial plasma concentration-time integral to Cp should be drawn. If the data are consistent with this model, then this graph will yield a curve that eventually becomes linear, with a slope of Ki and an ordinate intercept less than or equal to the vascular plus steady-state space of the reversible tissue region.

Use of cerebellar cGMP in the measurement and characterization of the diazepam/ethanol interaction.

The characterization and measurement of the benzodiazepine and ethanol interaction has been of major interest for many years. Various pharmacological and biochemical studies have been employed to investigate this interaction, which is believed to occur predominantly in the CNS, but localization of one particular brain area has not been investigated. This research employed the rat cerebellum as a site to study the diazepam/ethanol interaction. The measurement of cerebellar ethanol and diazepam, by gas chromatography, demonstrated an enhancement of diazepam levels by ethanol. Ethanol and diazepam, alone and in combination, displayed a significant depression of cerebellar 3',5'-Guanosine Cyclic Monophosphate (cGMP). The depression seen by the combination was significantly greater than the simple algebraic sum, but insignificantly different from the corrected algebraic sum. The double reciprocal plot of the data demonstrated a common ordinate intercept for the diazepam line and the diazepam/ethanol (2 g/kg) line, thus indicating a competitive mechanism of action.

Binding of high affinity heparin to antithrombin III. Stopped flow kinetic studies of the binding interaction.

The kinetics of high affinity heparin binding to human antithrombin III has been studied by stopped flow fluorimetry, using the 40% antithrombin fluorescence enhancement resulting from this interaction. At mu 0.15, pH 7.4, and 25 degrees C, the observed pseudo-first order rate constant varies hyperbolically with heparin concentration with a limiting rate constant of 440 +/- 90 s-1, demonstrating that heparin binding is a two-step process involving a conformational change in antithrombin III. An identical dependence is produced when antithrombin is varied, consistent with a symmetrical mechanism in which heparin binding induces a conformational change in antithrombin rather than perturbing an equilibrium between two conformational states of the protein. The rate constant for dissociation of the antithrombin-heparin complex is 1.1-1.5 s-1 at mu 0.15, as determined from the ordinate intercept at low heparin concentrations or by dissociation of the antithrombin-heparin complex with iodide. Observation of a single pseudo-first order binding rates over a 400-fold heparin concentration range with no detectable lags is compatible with the initial binding step being in rapid equilibrium with a KD of 4.3 +/- 1.3 X 10(-5) M at mu 0.15. Variation in ionic strength primarily affects the KD for the initial binding step with little effect on the conformational change rate constants, implying that binding involves ionic interactions. Calculation of the overall dissociation equilibrium constant from these rate parameters agrees with the directly determined value of 7.2 +/- 1.9 X 10(-8) M at mu 0.15. A major function of the conformational change is, thus, to increase the affinity of heparin for antithrombin III greater than 300-fold. The implications of these findings for the mechanism of the heparin-catalyzed inhibition of coagulation proteases by antithrombin III are discussed.

Diffusion with discontinuous swelling. V. Type II diffusion into sheets and spheres

AbstractType II diffusion into uniform spheres (radius R) and sheets (thickness 2l) is calculated under the assumption that the glass‐gel boundary proceeds at a constant velocity v from the surface towards the interior of the sample, that the diffusion coefficient Dg in the glass is constant and that the diffusion coefficient Dr of the rubbery gel is so much higher than vR or vl that practically no sorbate gradient is needed for the transport through the gel of the sorbate. The diffusion process is completed when this boundary reaches the center of the sample. The concentration profile of the sorbate in the glassy matrix in front of the boundary varies with time and velocity v. It does not, however, influence the boundary propagation velocity. Hence the often observed increase of the rate of the weight gain just at the end of the diffusion process is not considered at all. The relative weight gain of the sample W(t)/W∞ as a function of time is the only quantity usually measured. From the ordinate intercept A and the initial slope B of the plot of W(t)/t1/2W∞ vs. t1/2, one can calculate the characteristic transport properties, i.e., the diffusion coefficient Dg of the glass and the velocity v of the glass–gel boundary.

Effect of the pH on the degree of autolysis of Aspergillus niger

The effect of pH on the degree of autolysis of cultures of Aspergillus niger autolysed at different pH values has been studied. In each experiment the fungus was grown in a chemically defined medium until autolysis commenced. At that time the pH was adjusted to values of 2, 4, 6, 8, or 10 and automatically controlled at that pH throughout the autolytic period. A positive correlation (r = 0.77) between pH and the degree of autolysis was found. Linear regression analysis indicated that the data were fitted by a line of slope 2.53 and an ordinate intercept of 41.83.

Ellipsometric measurement of the Kerr magnetooptic effect

A conventional PCSA ellipsometer has been used to measure the transverse Kerr magnetooptic effect. The ellipsometer null was first obtained, and the ellipsometric psi and Delta were determined from this measurement. Then measurements were made as a function of polarizer angle while A =+/-ø. The magnetic field applied to the sample was square wave modulated, and both the dc and the modulated light intensities were measured. dI/I was a linear function of cos/(1 +/- sinØ), where ø = Delta - 2P. The ordinate intercept and the slope of the resulting straight line were the real and imaginary parts, respectively, of dr(p)/r(p). From psi, Delta, and dr(p)/r(p) the material quantities n and Q could be calculated.

Effect of salicylate on the binding of sulfonamides to bovine serum albumin.

Displacement of eight sulfonamides by sodium salicylate from the binding sites of bovine serum albumin (BSA) was studied by the equilibrium dialysis method at pH 7.4 and 37°. Amount of sulfonamides displaced by the addition of salicylate (1 or 3 mM) were linearly correlated with their amount bound to the binding sites of BSA in the absence of salicylate. Double-reciprocal plots of the binding of sulfamethoxazole to BSA with and without salicylate, following Langmuir's isotherms, resulted in linear curves with a common ordinate intercept. This result suggests that the inhibitory effects of salicylate on the binding of sulfamethoxazole to albumin were competitively performed at the same binding site on the protein.