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At least 37 records · Page 2Linked to original sources
PubMed1991

Structure-function relationships in the cysteine proteinases actinidin, papain and papaya proteinase omega. Three-dimensional structure of papaya proteinase omega deduced by knowledge-based modelling and active-centre characteristics determined by two-hydronic-state reactivity probe kinetics and kinetics of catalysis.

1. A model of the three-dimensional structure of papaya proteinase omega, the most basic cysteine proteinase component of the latex of papaya (Carica papaya), was built from its amino acid sequence and the two currently known high-resolution crystal structures of the homologous enzymes papain (EC 3.4.22.2) and actinidin (EC 3.4.22.14). The method used a knowledge-based approach incorporated in the COMPOSER suite of programs and refinement by using the interactive graphics program FRODO on an Evans and Sutherland PS 390 and by energy minimization using the GROMOS program library. 2. Functional similarities and differences between the three cysteine proteinases revealed by analysis of pH-dependent kinetics of the acylation process of the catalytic act and of the reactions of the enzyme catalytic sites with substrate-derived 2-pyridyl disulphides as two-hydronic-state reactivity probes are reported and discussed in terms of the knowledge-based model. 3. To facilitate analysis of complex pH-dependent kinetic data, a multitasking application program (SKETCHER) for parameter estimation by interactive manipulation of calculated curves and a simple method of writing down pH-dependent kinetic equations for reactions involving any number of reactive hydronic states by using information matrices were developed. 4. Papaya proteinase omega differs from the other two enzymes in the ionization characteristics of the common (Cys)-SH/(His)-Im+H catalytic-site system and of the other acid/base groups that modulate thiol reactivity towards substrate-derived inhibitors and the acylation process of the catalytic act. The most marked difference in the Cys/His system is that the pKa for the loss of the ion-pair state to form -S-/-Im is 8.1-8.3 for papaya proteinase omega, whereas it is 9.5 for both actinidin and papain. Papaya proteinase omega is similar to actinidin in that it lacks the second catalytically influential group with pKa approx. 4 present in papain and possesses a catalytically influential group with pKa 5.5-6.0. 5. Papaya proteinase omega occupies an intermediate position between actinidin and papain in the sensitivity with which hydrophobic interaction in the S2 subsite is transmitted to produce changes in transition-state geometry in the catalytic site, a fact that may be linked with differences in specificity in P2-S2 interaction exhibited by the three enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1979

[Kinetics and load distribution of supported free-end prostheses. IV. Effect of the saddle curvature on the saddle resp. abutment kinetics and the load distribution in prosthesis beds without abutments].

The influence of the saddle curvature on abutment tooth kinetics and abutment tooth stress was studied with unilateral rigid and movable free-end saddle dentures. The results showed that, independent of the length of the saddle and/or of the saddle curvature, considerable horizontal and vertical extrusive abutment tooth stress is present in addition to vertical intrusive abutment tooth stress. The saddle kinetics are basically influenced by the form of the saddle. The kinetics cannot be altered appreciably because of the mechanical characteristics of the connecting elements; it can only be surpressed at the cost of increased pier stress.

Biomechanical Phenomena↗
PubMed1978

Kinetics of plasma coagulation and lysis I: Basic kinetic model for time course of coagulation-lysis systems and its potential application to clinical studies.

The time courses of coagulation and coagulation-lysis were spectrophotometrically monitored after the addition of thrombin or thrombin-streptokinase to plasma, diluted 1:5 with normal saline, obtained from normal and presumably abnormal subjects. The kinetics of clotting, after an initial lag period of 0.5-1.5 min, demonstrated essentially first-order dependence on the amount of fibrinogen available to form the clot, and the asymptotic absorbance was independent of thrombin concentration. The rate of clotting was a function of added thrombin, and the ratios of the rate constants at 2.5 and 1.25 units of thrombin/ml of undiluted plasma were 1.65 +/- 0.03 SEM. At early times, the coagulation-lysis curve with thrombin-streptokinase could be superimposed on the clotting curve with thrombin alone for a given plasma with minor compensation for variable lag times. Subsequently, the curves diverged; lysis was monitored by the decrease in absorbance of the coagulation-lysis system. The rate of fibrinolysis increased with streptokinase concentration and was a function of the extent of lysis, and it permitted the description of the kinetics of lysis by a pseudoautocatalytic mechanism where the bimolecular rate constant appears proportional to streptokinase concentration. Ranges of clotting and lytic parameters for the plasma of normal subjects are given, and their potential use in diagnosing abnormalities is described.

Blood Coagulation↗
PubMed1977

Steady-state kinetics of electron transfer through cytochrome chain of uncoupled submitochondrial particles. I. General kinetic analysis.

Steady-state kinetics of electron transfer through the cytochrome chain of uncoupled ultrasonic submitochondrial particles at different pH values has been studied. Rate constants calculated from the Pring equation (ki' = V/PirPi+1ox) increased with the increase of the rate of the process. As in the previous work (Saks, V. A., Kupriyanov, V. V. and Luzikov, V. N. (1972) Biochim. Biophys. Acta 283, 42-53) this dependence was linear, but only at comparatively low rates of electron transfer. To explain the experimental data several kinetic models, based on the assumption that respiratory chains are activated when functioning, have been proposed and analysed. The best agreement with the experimental data was obtained for the model suggesting that the rate of activation of the carriers is directly proportional to the overall rate of electron transfer and to the proportion of non-activated respiratory chains in the system. Hence it appeared that electron transfer through already activated chains entailed activation of adjacent non-activated chains. This model allowed rate constants for non-activated (ki) and activated (ki) states of the carriers, as well as the life-time of the activated carriers (tau) to be determined.

Animals↗
PubMed1975

[The pharmaco-kinetics of angiographic contrast media with special reference to the extra-vascular spaces. Fundamental studies on dog for the characterisation of angiographic media. I The pharmaco-kinetics of various contrast media under conditions of constant infusion (balanced flow)].

The pharmaco-kinetics of angiographic contrast media in the extra-vascular space, which are largely unknown, were investigated experimentally in dogs. As part of a basic study, using radio-active contrast media, it was possible to determine the concentration and rate of elimination in practically all organs and tissues. Measurements were carried out first after prolonged infusion of the contrast under conditions of balanced flow, and secondly six hours after the end of the infusion. It was therefore possible to determine the inflow and loss of contrast medium in various organs, or organs systems. The most commonly used angiographic contrast media in Germany were investigated. Their kinetic behaviour is largely identical, their pattern of distribution and elimination depended principally on the organ or tissue. A comprehensive discussion of the results of all the experiments will be given in the third article.

Animals↗
PubMedDate not supplied

Myocardial bethanidine kinetics after single-dose intravenous infusion: correlation with plasma kinetics in closed-chest dogs.

Myocardial and plasma bethanidine kinetics were determined in five dogs after an intravenous dose of 6 mg/kg/10 min. Serial myocardial drug concentrations were determined from endomyocardial samples obtained by transvenous biopsies between 15 min and 72 h. Tissue and plasma samples were assayed by gas-liquid chromatography. Bethanidine was rapidly concentrated in myocardium within 15 min. Tissue/plasma drug ratios averaged 131 +/- 35 between 15 min and 2 h and 53 +/- 10 between 6 and 48 h. Parallel biexponential decay then occurred for both tissue and plasma compartments; the terminal half-life approximated 16 h. Based on differences in rates of myocardial drug kinetics, the cardiac antifibrillatory effects of bethanidine may occur more rapidly than those of bretylium.

Animals↗
PubMed1975

Matrix simulation of duodenal crypt cell kinetics. II. Cell kinetics following hydroxyurea.

The perturbed cellular kinetics of the duodenal crypt following a single injection of hydroxyurea (HU) have been simulated using matrix algebra. Following the direct effects of HU (S-phase cytotoxicity and a G1/S block) the crypt cell kinetics undergo several alterations. Previously documented alterations include: (1) a temporary partial synchronization of the surviving cells, (2) a shortening of the cell-cycle transit time, and (3) recruitment of normally non-proliferating cells into active proliferation. These conclusions have been extended by constructing several different complex but theoretically possible recovery models and the validity of each of these models has been evaluated by simulating the following biological data: the number of cells in the S and M-phase of the cell cycle, total viable cells per crypt, and the per cent labeled mitosis and the number of labeled cells following 3H-TdR injections at 9 and 21 hr after HU treatment. The model which showed visually the best overall agreement with all sets of the data was chosen as "most probable' and leads to the following interpretations. Immediately after the end of the HU block (i.e. 5 hr after HU injection) the modal cell-cycle transit time is reduced to 8 hr. By 17 hr after HU, the modal transit time is increased to 10 hr. Repopulation of the proliferating compartment, i.e. restoration of the proliferating compartment back to the control value, occurs between 12 and 17 hr after HU injection and probably consists of both recycling of the proliferating cells (i.e. they do not progress up into the non-proliferating compartment) and recruitment of the non-proliferating cells into active proliferation. Also, the rate at which the non-proliferating cells move onto the villi is reduced temporarily. The overall recovery process results in a crypt which temporarily is larger than control and produces villi cells at a rate which is faster than the control. The time when the crypt size and villus cell production rate return to normal cannot be established using the available data.

Animals↗
PubMed1975

Investigations on the kinetic mechanism of octopine dehydrogenase. 1. Steady-state kinetics.

The kinetic mechanism of action of octopine dehydrogenase was investigated. This enzyme catalyses the reversible dehydrogenation of D-octopine to L-arginine and pyruvate, in the presence of nicotinamide-adenine dinucleotide. Initial velocity and product inhibition studies were carried out in both directions. Most of the results are consistent with a bi-ter sequential mechanism where NAD+ binds first to the enzyme followed by D-octopine, and the products are released in the order L-arginine, pyruvate and NADH. Various kinetic parameters were determined for each reactant at 33 degrees C, at pH 9.6 for NAD reduction, at pH 6.6 for NADH oxidation.

Animals↗
PubMed1976

[Steady-state kinetics of electron transfer through the cytochrome chain of uncoupled submitochondrial particles. General kinetic analysis].

Steady-state kinetics of electron transfer through the cytochrome chain of uncoupled ultrasonic submitochondrial particles at different pH values were studied. The rate constants calculated according to Pring's equation (k1=V/Prpoxt i+1) were found to increase linearly with the increase in the rate of electron transfer. Linearity was observed, however, only at relatively low rates of electron transfer. Several kinetic models were developed and analysed to fit the experimental data on the basis of the suggested activation of respiratory chains induced by their functioning. The best agreement with the experimental data was obtained with the model implying that the rate of activation of the electron carriers is directly proportional to the overall rate of electron transfer and the portion of non-activated respiratory chains in the system. It followed therefrom that electron transfer through already activated chains induced activation of adjacent non-activated chains. This model made it possiple to determine the rate constants for non-activated (ki) and activated (k) carrier states and the life-times of activated carriers (tau).

Animals↗
PubMed1976

Kinetics and mechanism of degradation of some 5-allylbarbituric acid derivatives. Part 3: Kinetics of solvolysis of major intermediates of 5.5-diallylbarbituric acid degradation.

Solvolysis of N-diallylacetylurea and 5.5-diallylmalonuric acid was investigated in the pH range ca. 8--12 by means of spectrophotometric and t.l.c. methods. Their log k--pH profiles were constructed from the experimental results obtained by degradation at 70 degrees C. Therefore, specific catalytic rate constants and pKa's were derived. The kinetic mechanism of N-diallylacetylurea solvolysis, resulting among other things from the so-called kinetic salt effect, depends on hydroxyl-ion attack on its undissociated and monoanionic forms. However, the degradation of alpha.alpha-diallylmalonuric acid in the pH range 10--12 is an example of specific base catalysis which can be explained by hydroxyl-ion attack on its monoanionic species. The degradation of alpha.alpha-diallylmalonuric acid below pH=10 does not follow a theoretical equation postulated, because the spectrophotometric method does not allow monitoring the formation of N-diallylacetylurea in the presence of the above acid. Thin-layer chromatography was used to check different pathways of transformations of the intermediate studies.

Allyl Compounds↗
PubMed1990

Unusual transient- and steady-state kinetic behavior is predicted by the kinetic scheme operational for recombinant human dihydrofolate reductase.

Association and dissociation rate constants obtained by stopped-flow spectroscopy have permitted definition of a kinetic scheme for recombinant human dihydrofolate reductase that correctly predicts full time course kinetics of the enzymatic reaction over a wide range of substrate and product concentrations. The scheme is complex compared with that for the bacterial enzyme and involves branched pathways. It successfully accounts for observed rapid hysteresis preceding steady state and for the nonhyperbolic dependence of steady-state rate on substrate and product concentrations. The major branch point in the catalytic cycle occurs at E.NADP.H4folate because either NADP or H4folate can dissociate from the ternary product complex (koff = 84 s-1 and 46 s-1, respectively). The rate of conversion of enzyme-bound substrates to products is very fast (k = 1360 s-1) and nearly unidirectional (Kequ = 37) so that other steps limit the catalytic rate. At saturating substrate concentrations these steps include release of NADP and H4folate from E.NADP.H4folate and release of products from the two abortive complexes E.NADPH.H4folate (koff = 225 s-1) and E.NADP.H4folate (koff = 4.6 s-1). Since NADP dissociates slowly from E.NADP.H2folate nearly 90% of the enzyme accumulates as this complex at steady state. Nonetheless, the catalytic rate is maintained at 12 s-1 by rapid flux of a small portion of the enzyme through an alternate branch. At physiological concentrations of substrates and products the steady-state rate is limited primarily by the rate of H2folate binding to E.NADPH so that the enzyme is extremely efficient.

Humans↗
PubMed1975

Kinetic studies of carboxypeptidase Y. I. Kinetic parameters for the hydrolysis of synthetic substrates.

Kinetic parameters for carboxypeptidase Y [EC 3.4.12.1], characterized as a nonspecific enzyme, are given for the hydrolysis of a series of acylated peptides, acylated amino acid esters, and amides. We confirmed that the enzyme released COOH-terminal proline and beta-alanine at an appreciable rate, as well as neutral amino acids with aromatic and aliphatic side chains at a very high speed. The rates of hydrolysis of ester and amide substrates were compatible with those produced by chymotrypsin [EC 3.4.21.1]. Stereospecificity was also demonstrated by the failure to hydrolyze peptide, ester, amide, and anilide substrates containing a D-amino acid. The effects of pH, solvents, and salt concentrations on the kinetic parameters of hydrolysis of peptide and ester substrates are also described.

Anilides↗
PubMed1976

Kinetics of drug decomposition. Part 38. Hydrolysis and autoxidation of sodium phenylbutazone and aminophenazone in binary kinetic system.

The kinetics of hydrolysis and autoxidation of sodium phenylbutazone (PhB-Na) and aminophenazone (APh) was studied in ammonia-acetate, Carmody and Welford buffers at different buffer concentration, pH, ionic strengths and temperatures. The reaction in N2 atmosphere and under a constant O2 pressure, carried out in calibrated ampoules, followed the first order reaction kinetics. The assay of PhB-Na and APh in the presence of their degradation produces was carried out spectrophotometrically in the degraded solutions.

Aminopyrine↗
PubMed1991

Analysis of kinetic data in transport studies: new insights from kinetic studies of Na(+)-D-glucose cotransport in human intestinal brush-border membrane vesicles using a fast sampling, rapid filtration apparatus.

Using the fast sampling, rapid filtration apparatus (FSRFA) recently developed in our laboratory (Berteloot et al., 1991, J. Membrane Biol. 122:111-125), we have studied the kinetic characteristics of Na(+)-D-glucose cotransport in brush-border membrane vesicles isolated from normal adult human jejunum. True initial rates of transport have been determined at both 20 and 35 degrees C using a dynamic approach which involves linear-regression analysis over nine time points equally spaced over 4.5 or 2.7 sec, respectively. When the tracer rate of transport was studied as a function of unlabeled substrate concentrations added to the incubation medium, a displacement curve was generated which can be analyzed by nonlinear regression using equations which take into account the competitive inhibition of tracer flux by unlabeled substrate. This approach was made imperative since at 20 degrees C, in the presence of high substrate concentrations or 1 mM phlorizin, no measurable diffusion was found and the resultant zero slope values cannot be expressed into a classical v versus S plot. All together, our results support the existence of a single Na(+)-D-glucose cotransport system in these membranes for which Na+ is mandatory for uptake. This conclusion is at variance with that of a recent report using the same preparation (Harig et al., 1989. Am J. Physiol. 256:8618-8623). Since the discrepancy seems difficult to resolve on the consideration of experimental conditions alone, we have determined the kinetic parameters of D-glucose transport using one time point measurements and linear transformations of the Michaelis-Menten equation, in order to investigate the potential problems of such a widely used procedure. Comparing these approaches, we conclude that: (i) the dynamic uptake measurements give a better understanding of the different uptake components involved: (ii) it does not matter whether a dynamic or a one time point approach is chosen to generate the uptake data provided that a nonlinear-regression analysis with proper weighting of the data points is performed; (iii) analytical procedures which rely on linearization of Michaelian process(es) are endowed with a number of difficulties which make them unsuitable to resolve multicomponent systems in transport studies. A more general procedure which uses a nonlinear-regression analysis and a displacement curve is proposed since we demonstrate that it is far superior in terms of rapidity, data interpretation, and visual information.

Biological Transport↗
PubMed1975

[The pharmaco-kinetics of angiographic contrast media, with special reference to the extra-vascular space. An experimental study on dogs. Paper II. Pharmaco-kinetics of an angiographic contrast medium used for selective angiography (author's transl)].

Basic studies were carried out on experimental animals in order to investigate the pharmaco-kinetics of angiographic contrast media when used in various ways. Injections were carried out through angiographic catheters in a "physiological angiographic" manner. Measurements obtained by using radioactive compounds have shown that the distribution and excretion of the contrast medium are independent of the site of injection. The kinetics of the contrast within an organ do not differ, whether it is injected selectively or not. The results of all the experiments will be discussed at the conclusion of the third paper.

Angiography↗
PubMed1992

[Kinetics of vaccination antibodies against tetanus toxoid, diphtheria toxoid, measles virus, poliomyelitis virus and pneumococcus after allogenic and autologous bone marrow transplantation and booster vaccination. 2: Kinetics of vaccination antibodies against diphtheria toxoid after allogenic and autologous bone marrow transplantation].

In the second part of the paper we report on the results of the diphtheria antitoxin valuation of 8 children after allogeneic bone marrow transplantation (BMT) with and without graft versus host disease (GvHD) as well as on the kinetics of the diphtheria antitoxin of 5 children after allogeneic BMT with and without GvHD and of 5 children after autologous transplantation. The antibody valuation was done by a cell-culture assay. Whereas the inspection of the isolated data gives the impression of a swift antibody decrease up to the non-protective level from the 7th month after BMT, the kinetic tests are more highly differentiated. Besides rapidly decreasing values below the accepted protection rate of 0.01 IU/ml in the allogeneic transplanted groups, there are patients with positive antibody titres within an observation period of up to 24 months after BMT in the allogeneic as well as in the autologous transplantation group.

Bone Marrow Transplantation↗
PubMed1992

[Kinetics of vaccine antibodies to tetanus toxoid, diphtheria toxoid, measles virus, poliomyelitis virus and pneumococci after allogenic and autologous bone marrow transplantation and booster immunization. 1: The kinetics of vaccine antibodies to tetanus toxoid after allogenic and autologous bone marrow transplantation].

Today BMT belongs to the established methods of treatment in haematology and oncology. Because of the constant increase of healthy long-term survivors after BMT the problem of immunological reconstitution and eventual possible late effects gets more and more importance. One problem, which til now has been few attention paid to, is that of the protection by vaccination after BMT. We report on the kinetics of the tetanus-antitoxin in 20 patients after allogeneic or autologous BMT and demonstrate the influence of a graft-versus-host disease and its therapy on the antibody kinetics. In the group of allogeneic transplanted children without a GvHD the tetanus-antitoxin titers felt below their detection range after a time of about 8 months whereas in the group with GvHD this effect already occurred after nearly 4 months. The autologous transplanted patients have a positive antibody level til the time of 20 months after BMT. As a consequence of the lost protection by vaccination after BMT follows the necessity of revaccinations respectively of boostering after immunological reconstitution.

Adolescent↗