SEARCH · PubMed Health

Results for “Kinetics”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources

PubMed2003

Equilibrium and kinetics of the allosteric transition of GroEL studied by solution X-ray scattering and fluorescence spectroscopy.

We have studied the ATP-induced allosteric structural transition of GroEL using small angle X-ray scattering and fluorescence spectroscopy in combination with a stopped-flow technique. With X-ray scattering one can clearly distinguish the three allosteric states of GroEL, and the kinetics of the transition of GroEL induced by 85 microM ATP have been observed directly by stopped-flow X-ray scattering for the first time. The rate constant has been found to be 3-5s(-1) at 5 degrees C, indicating that this process corresponds to the second phase of the ATP-induced kinetics of tryptophan-inserted GroEL measured by stopped-flow fluorescence. Based on the ATP concentration dependence of the fluorescence kinetics, we conclude that the first phase represents bimolecular non-cooperative binding of ATP to GroEL with a bimolecular rate constant of 5.8 x 10(5)M(-1)s(-1) at 25 degrees C. Considering the electrostatic repulsion between negatively charged GroEL (-18 of the net charge per monomer at pH 7.5) and ATP, the rate constant is consistent with a diffusion-controlled bimolecular process. The ATP-induced fluorescence kinetics (the first and second phases) at various ATP concentrations (< 400 microM) occur before ATP hydrolysis by GroEL takes place and are well explained by a kinetic allosteric model, which is a combination of the conventional transition state theory and the Monod-Wyman-Changeux model, and we have successfully evaluated the equilibrium and kinetic parameters of the allosteric transition, including the binding constant of ATP in the transition state of GroEL.

Adenosine Triphosphate↗

PubMed1992

Schematic methods for probabilistic enzyme kinetics.

The theory of steady-state enzyme processes which avoids using the mass action law of chemical kinetics and consistently describes catalytic mechanisms by probabilistic concepts has recently been proposed (Mazur, 1991, J. theor. Biol. 148, 229-242). To facilitate the analysis of complex reaction graphs by this theory the possibility of constructing schematic rules similar to those used in classical kinetics is studied. It is found that due to the similarity of algebraic procedures the popular method of King & Altman can be applied in probabilistic kinetics in addition to the earlier proposed rule based on enumeration of cycles of the reaction graph. This similarity also allows one to adapt many other shortcut methods of classical kinetics for probabilistic reaction graphs. The paper considers separately the possibility of transforming reaction mechanisms so that the initial graph is replaced by a simpler but equivalent one. It is shown that there are few cases when a group of states can be replaced by one united state, with earlier known rules such as the rule of Cha for equilibrium stages being particular cases of a more general procedure. In addition a novel method is proposed which performs step-by-step reduction of any reaction graph. All the new methods can be adapted for traditional kinetics as well. The results obtained demonstrate that many schematic rules of classical kinetics are of probabilistic origin.

Enzymes↗

PubMed1996

Glucose and lactate kinetics during a short exercise bout in pregnancy.

Pregnancy is considered diabetogenic. Although exercise has been advocated to assist in metabolic control of the nonpregnant diabetic individual, there is a paucity of data about the metabolic effects of exercise during pregnancy. To examine whether moderate exertion may be beneficial in the maintenance of maternal carbohydrate homeostasis, glucose and lactate kinetics were measured in the third trimester in five pregnant nondiabetic women (gestational age, 34.2 +/- 0.1 weeks [mean +/- SE]) by infusion of 45 microg x kg(-1) x min(-1) [6,6-2H2]glucose and 70 microg x kg(-1) x min(-1) [U-13C]lactate tracers. Subjects were observed at rest for determination of baseline steady-state kinetics over a 30-minute period, and then they exercised for 30 minutes at 60% maximum oxygen consumption (VO2max) and were evaluated for 30 minutes postexercise. Glucose and lactate kinetics and lactate oxidation were measured throughout the exercise protocol. This study was repeated postpartum in all individuals at least 6 weeks after delivery. Compared with the steady-state preinfusion period, plasma glucose concentration was not elevated during exercise in either group, nor was plasma lactate concentration significantly different in either group. Glucose kinetics did not change during exercise, but lactate kinetics increased in both groups. V02 and percent of lactate C contribution to CO2, an indication of lactate oxidation, increased proportionally in both groups during exercise. Metabolic perturbations, as measured by glucose and lactate kinetics, do not appear to be different during the third trimester of pregnancy during a relatively short bout of exercise compared with the nonpregnant state.

Adult↗

PubMed2003

Kinetic modeling of a mixed culture of Pseudomonas denitrificans and Bacillus subtilis under aerobic and anoxic operating conditions.

The kinetics of biological denitrification have been studied and several models, with varying degree of complexity, to be used for design purposes have been presented in the recent years. However, most of these kinetic studies were performed with mixed (and not well defined) microbial systems, such as activated sludge. In the present work, kinetic experiments were carried out in order to study the dynamic characteristics of a defined mixed culture of the denitrifiers Pseudomonas denitrificans and Bacillus subtilis under anoxic and aerobic conditions in a defined synthetic medium involving a mixture of organic substrates, in the presence of nitrates and/or nitrites. Denitrification was assumed to occur by the consecutive reduction of nitrates to nitrites and then to nitrogen gas without accumulation of intermediate gaseous products. The behavior of these defined mixed cultures was predicted using a kinetic model based on the kinetic models that have already been developed for each bacterium separately and the predictions were compared with the results from mixed culture experiments. The overall mathematical model that was developed and validated in the present work is capable of describing the behavior of the mixed culture in the above conditions, i.e. the nitrates and nitrites reduction kinetics, the cell growth, and the organic carbon utilization rates.

Bacillus subtilis↗

PubMed2002

Polymerization kinetics of HEMA/DEGDMA: using changes in initiation and chain transfer rates to explore the effects of chain-length-dependent termination.

The effect of kinetic chain length and chain transfer on the polymerization kinetics and network structure in polymerizations of loosely crosslinked 2-hydroxyethyl methacrylate/di(ethylene glycol) dimethacrylate mixtures was explored. Polymerization behavior of the monomer mixture in the presence and absence of a chain transfer agent was monitored at various initiation rates and chain transfer agent concentration levels. Dependence of the polymerization rate on the initiation rate was found to deviate from the classical square-root relationship because of chain-length-dependent termination. This effect was further confirmed by addition of a chain transfer agent. The presence of a chain transfer agent led to the formation of shorter kinetic chains, which enhanced termination and slowed the polymerization. Investigation of the polymerization kinetics after cessation of irradiation yielded kt/kp[M] values for both systems. Prior to the onset of reaction diffusion-controlled termination, the system that included a chain transfer agent exhibited much higher kt/kp[M] values than the polymerization system without added chain transfer agent. In addition, the onset of reaction diffusion-controlled termination was delayed to higher conversions in the system containing chain transfer agent. The impact of a chain transfer agent on the polymerization behavior and kinetics demonstrates that the chain-length-dependent termination phenomenon is indeed important and must be considered in kinetic modeling of loosely crosslinked systems.

Calorimetry, Differential Scanning↗

PubMed2001

The interaction between membrane kinetics and membrane geometry in the transmission of action potentials in non-uniform excitable fibres: a finite element approach.

By solving the partial differential equations for an axonal segment using a finite element method, the interaction between membrane kinetics and axonal inhomogeneities, measured by their influence on propagated action potentials and stochastic spike trains, is investigated for Morris-Lecar and Hodgkin-Huxley membrane models. To facilitate comparisons of both kinetic models, parameter values are matched to give approximately the same speed for propagated action potentials. In all cases examined, the Morris-Lecar membrane model is more sensitive to geometric inhomogeneities than the comparable Hodgkin-Huxley membrane model. This difference in sensitivity can, in part, be attributed to significant differences in the membrane current supplied by each kinetic model ahead of the action potential. Also, the Morris-Lecar membrane model did not generate reflected action potentials whereas these were observed over a narrow range of geometric parameters for the comparable Hodgkin-Huxley membrane model. Simulations using stochastic spike train input showed that the presence of a sharp flare could significantly modify the statistical characteristics of the spike train output. The behaviour of action potentials governed by Morris-Lecar kinetics were more sensitive to changes in axonal geometry than those generated by comparable Hodgkin-Huxley kinetics. As a consequence of the fine balance between membrane kinetics and axon geometry, local changes in membrane properties, such as those caused by synaptic activity, can be expected to have a strong influence on the behaviour of stochastic spike trains at regions of changing axonal geometry.

Action Potentials↗

PubMed1997

Kinetics of serum prostate-specific antigen after external beam radiation for clinically localized prostate cancer.

BACKGROUND AND PURPOSE: To determine the kinetics of serum prostate-specific antigen (PSA) after radiation therapy of localized prostate cancer and to evaluate whether such kinetics provide prognostic information. MATERIALS AND METHODS: Eight hundred forty-one men with serial PSA determinations who underwent external beam radiation without androgen ablation were analyzed to determine postradiation PSA kinetic parameters (half-life and doubling time) and to correlate these parameters with disease outcome. Non-linear regression techniques were used to determine half-lives and doubling times. RESULTS: The postradiation serum PSA data fitted well to first order kinetic models. The median PSA half-life was 1.6 months (range 0.5-9.2 months). There was no correlation between half-life and T-stage or Gleason grade. A significant but quantitatively weak correlation was present between the pretreatment PSA level and half-life; lower pretreatment levels were associated with longer half-lives. Half-life did not correlate with disease outcome whether the endpoint was local recurrence, distant metastasis or rising PSA. In 263 men with a rising postradiation PSA profile the median PSA doubling time was 12.2 months (range 0.8-80.2 months). Faster doubling times were significantly associated with higher T-stage, higher Gleason grade and higher pretreatment PSA levels. Thus, patients with initially adverse disease developed faster rising PSA values after treatment than patients with less adverse disease. The most striking correlation was between rapid doubling time and the likelihood of metastatic relapse. Patients who developed metastases had a median PSA doubling time of 4.2 months compared to a median doubling time of 11.7 months in patients who developed local recurrence. Overall, patients with a PSA doubling time of less than 8 months had a 7-year actuarial metastatic rate of 54%, while patients with a PSA doubling time exceeding 8 months had only a 7% metastatic rate. Particularly ominous was the combination of a doubling time shorter than 8 months which began to rise within the first year; by 3 years 50% of these men had metastases and all were actuarially projected to develop such relapse by 6.5 years. CONCLUSIONS: Overall, the clinical utility of postradiation serum PSA kinetics was small. There were no discernible uses for PSA half-life. In patients with a rising PSA profile the faster the kinetics the more adverse the disease. Doubling times shorter than 8 months, especially if the rise begins in the first year, predict for metastatic relapse. However, in the absence of decisively useful treatment for metastatic prostate cancer the virtues of the early detection of metastases remain unclear.

Aged↗

PubMed1996

Cytochrome P450 conformation and substrate interactions as probed by CO binding kinetics.

The kinetics of CO binding to cytochrome P450, as measured by the flash photolysis technique, is a powerful probe of P450 structure-function relationships. The kinetics are sensitive to P450 conformation and dynamics and are modulated by P450 interactions with substrates and other components of the microsomal membrane. Application of a difference method to kinetic data analysis distinguishes the kinetic behavior of individual P450 forms in the microsomal membrane. This approach shows that substrates differentially modulate the kinetics via: 1) changes in P450 conformation/dynamics that either accelerate or reduce the binding rate; and/or 2) steric effects that reduce the rate. Both mechanisms are observed, the relative contributions of each varying in a substrate- and P450-dependent manner. In addition to microsomes, substrate interactions with individual P450s can be similarly probed using expressed P450s. Experiments with baculovirus-expressed human P450 3A4 show that this P450 consists of multiple conformers with distinct substrate specificities, an observation which provides a basis for its recognition of a wide array of structurally diverse substrates. These studies thus demonstrate the utility of CO binding kinetics in elucidating fundamental P450-substrate interactions in a biological membrane environment.

Animals↗

PubMed2001

Plasma progesterone kinetics following surgical treatment of ectopic pregnancies.

OBJECTIVES: Comparative study of plasma progesterone and betaHCG kinetics following surgical treatment of ectopic pregnancy. STUDY DESIGN: Prospective study involving 62 patients with tubal ectopic pregnancies. Study of the kinetics of plasma progesterone and betaHCG, and the correlation coefficient between plasma progesterone and betaHCG levels during post-operative follow-up. RESULTS: Thirty-nine patients were treated by salpingostomy and 23 by salpingectomy. Analyzing the betaHCG kinetics according to treatment revealed that both curves were convergent on day 2. Progesterone kinetics differed greatly in that they appeared "parallel and confused". Analyzing the correlation between betaHCG and progesterone levels proved the absence of a significant link. CONCLUSIONS: Studying the kinetics of plasma progesterone after surgical treatment of ectopic pregnancies revealed a fast decrease in progesterone. Statistical analysis of the progesterone concentration showed that post-operative kinetics is fully independent from that of betaHCG. Progesterone therefore cannot be substituted to betaHCG for post-operative follow-up.

Chorionic Gonadotropin, beta Subunit, Human↗

PubMed2002

Kinetics of iron release from pig spleen ferritin with bare platinum electrode reduction.

Several anaerobic electrochemical cells were employed to study the kinetics of iron release from pig spleen ferritin (PSF) at a bare platinum electrode. Controlled potential microcoulometry (CPM) is the principal technology used to investigate the kinetics in the absence of a mediator. A kinetic study of iron release by microcoulometry has revealed that ferritin undergoes direct electron transfer at the electrode in the absence of a mediator, indicating that ferritin is an electroactive protein. Several experiments failed to show that alpha'alpha-bipyridyl has the capacity to reduce hydrolyzed Fe(3+) within the ferritin core after it has been reduced by the electrode at -600 mV vs. NHE in the absence of mediator. PSF is known to bind heme to generate a hemeoprotein, named pig spleen hemeoferritin (PSF(ho)). The rate of iron release is accelerated by the heme binding to PSF(ho) without the need for small mediators. Under similar conditions, two kinetic processes for iron release from PSF and bacterial ferritin of Azoaobacter vinelandii (AvBF) were studied and both fit a zero-order law. In addition, the rate of iron release in PSF can be accelerated two-fold by a specific reduction system consisting of ascorbic acid (AA) and the bare platinum electrode at -600 mV. However, this kinetic process does not follow zero-, half-, first, or second-order rate laws. A model is proposed to explain a mechanism of direct electron transfer between ferritin and the electrode is derived to describe the kinetics of iron release.

Animals↗

PubMed2001

Oxidation of p-hydroxybenzoic acid by UV radiation and by TiO2/UV radiation: comparison and modelling of reaction kinetic.

The phenolic compound p-hydroxybenzoic acid is very common in a great variety of agroindustrial wastewaters (olive oil and table olive industries, distilleries). The objective of this work was to study the photocatalytic activity of TiO2 towards the decomposition of p-hydroxybenzoic acid. In order to demonstrate the greater oxidizing power of the photocatalytic system and to quantify the additional levels of degradation attained, we performed experiments on the oxidation of p-hydroxybenzoic acid by UV radiation alone and by the TiO2/UV radiation combination. A kinetic model is applied for the photooxidation by UV radiation and by the TiO(2)/UV system. Experimental results indicated that the kinetics for both oxidation processes can be fitted well by a pseudo-first-order kinetic model. The second oxidation process can be explained in terms of the Langmuir-Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K(pHB), and the second order kinetic rate constant, k(c), were 0.37 ppm(-1) and 6.99 ppm min(-1), respectively. Finally, a comparison between the kinetic rate constants for two oxidation systems reveals that the constants for the TiO2/UV system are clearly greater (between 220-435%) than those obtained in the direct UV photooxidation.

Catalysis↗

PubMed2003

Kinetics of degradation of 4-imidazolidinone prodrug types obtained from reacting prilocaine with formaldehyde and acetaldehyde.

The kinetics of decomposition of 4-imidazolidinone prodrug types obtained by reacting prilocaine (I) with formaldehyde and acetaldehyde has been studied in aqueous solution in the pH range 1-7.4 at 60 and 37 degrees C, respectively. At pH<5 the hydrolysis of the derivative derived from formaldehyde (II) to yield I obeyed apparent first-order kinetics. At higher pH, the decomposition reactions proceeded to an equilibrium and the reactions could be described by first- and second-order reversible kinetics. A plot of the logarithm of the apparent first-order rate constants for hydrolysis of II against pH resulted in a sigmoidal-shaped pH-rate profile characteristic for the hydrolysis of many N-Mannich bases. A half-life at pH 7.4 (60 degrees C) of 6.9h for compound II was calculated. Compared to II the 4-imidazolidinone derived from acetaldehyde (III) exhibited enhanced instability in aqueous buffer solutions. The decomposition was followed at 37 degrees C monitoring the decrease in concentration of intact (III). At acidic pH the reactions displayed strict first-order kinetics and the disappearance of III was accompanied by a concomitant formation of I. At pH 7.4, the rate data also applied reasonably well to first-order kinetics despite the observation that small amounts of III was formed at pH 7.4 from a solution containing equimolar concentrations of acetaldehyde and prilocaine (10(-4)M). In case of III, a bell-shaped pH-rate profile was obtained by plotting the logarithm of the pseudo-first-order rate constants against pH indicating the involvement of a kinetically significant intermediate in the reaction pathway and a change of the rate-limiting step in the overall reaction with pH. For the stability studies performed at pH 6.9 and 7.4 product analysis revealed that parallel to formation of (I) an unknown compound (X) emerged. Compared to III, compound X is hydrolysed to give I at a slower rate (t(50%)=30 h at 37 degrees C). Based on LC-MS data it is suggested that (X) is an isomeric form of III, which may exist in four diastereomeric forms. Thus, at physiological pH an initial relatively fast regeneration of I from III is to be expected followed by a slower drug activation resulting from hydrolysis of the isomeric form of III.

Acetaldehyde↗

PubMed1999

Hydroiodic acid attachment kinetics as a chemical probe of gaseous protein ion structure: bovine pancreatic trypsin inhibitor.

The kinetics of attachment of hydroiodic acid (HI) to the (M + 6H)6+ ions of native and reduced forms of bovine pancreatic trypsin inhibitor (BPTI) in the quadrupole ion trap environment are reported. Distinctly nonlinear (pseudo first-order) reaction kinetics are observed for reaction of the native ions, indicating two or more noninterconverting structures in the parent ion population. The reduced form, on the other hand, shows very nearly linear reaction kinetics. Both forms of the parent ion attach a maximum of five molecules of hydroiodic acid. This number is expected based on the amino acid composition of the protein. There is a total of 11 strongly basic sites in the protein (i.e., six arginines, four lysines, and one N-terminus). An ion with protons occupying six of the basic sites has five available for hydroiodic acid attachment. The kinetics of successive attachment of HI to the native and reduced forms of BPTI also differ, particularly for the addition of the fourth and fifth HI molecules. A very simple kinetic model describes the behavior of the reduced form reasonably well, suggesting that all of the neutral basic sites in the reduced BPTI ions have roughly equal reactivity. However, the behavior of the native ion is not well-described by this simple model. The results are discussed within the context of differences in the three-dimensional structures of the ions that result from the presence or absence of the three disulfide linkages found in native BPTI. The HI reaction kinetics appears to have potential as a chemical probe of protein ion three-dimensional structure in the gas phase. Hydroiodic acid attachment chemistry is significantly different from other chemistries used to probe three-dimensional structure and hence, promises to yield complementary information.

Acids↗

PubMed1995

Dialysate-based kinetic modeling.

The focus of this review article is urea kinetic modeling based on the exploitation of concentration measurements in the spent dialysate stream. After a review of blood-based urea kinetic modeling, dialysate-based techniques are considered, beginning with dialysate collection techniques and their associated urea kinetic modeling equations. Partial dialysate collection methods and equations for the determination of protein catabolic rate based on a 7-day mass balance period are explored next. This is followed by a description of urea sensors and their application for dialysate-based modeling including the determination of protein catabolic rate, predialysis blood urea nitrogen (BUN), and KT/V. How the output of a urea sensor may allow the detection of significant changes in patient clearance during the course of dialysis is illustrated, as well as how double-pool urea kinetics may be accounted for in KT/V determination. Routine determination of patient lean body mass using creatinine kinetic modeling based on partial dialysate collection or a dialysate-based creatinine concentration sensor is demonstrated. Finally, the potential for complete automation of urea kinetic modeling in dialysis machines of the future is explored.

Blood Urea Nitrogen↗

PubMed1997

Kinetics and mechanism of amyloid formation by the prion protein H1 peptide as determined by time-dependent ESR.

BACKGROUND: Peptides derived from three of four putative alpha-helical regions of the prion protein (PrP) form amyloid in solution. These peptides serve as models for amyloidogenesis and for understanding the alpha helix -->beta strand conformational change that is responsible for the development of disease. Kinetic studies of amyloid formation usually rely on the detection of fibrils. No study has yet explored the rate of monomer peptide uptake or the presence of nonfibrillar intermediate species. We present a new electron spin resonance (ESR) method for probing the kinetics of amyloid formation. A spin label was covalently attached to a highly amyloidogenic peptide and kinetic trials were monitored by ESR. RESULTS: Electron microscopy shows that the spin-labeled peptide forms amyloid, and ESR reveals the kinetic decay of free peptide monomer during amyloid formation. The combination of electron microscopy and ESR suggests that there are three kinetically relevant species: monomer peptide, amyloid and amorphous aggregate (peptide aggregates devoid of fibrils or other structures with long-range order). A rather surprising result is that amyloid formation requires the presence of this amorphous aggregate. This is particularly interesting because PrPSc, the form of PrP associated with scrapie, is often found as an aggregate and amyloid formation is not a necessary component of prion replication or pathogenesis. CONCLUSIONS: Kinetic analysis of the time-dependent data suggests a model whereby the amorphous aggregate has a previously unsuspected dual role: it releases monomer into solution and also provides initiation sites for fibril growth. These findings suggest that the beta-sheet-rich PrPSc may be stabilized by aggregation.

Amyloid↗

PubMed2001

Kinetic analysis of enzyme systems with suicide substrate in the presence of a reversible competitive inhibitor, tested by simulated progress curves.

The use of suicide substrates remains a very important and useful method in enzymology for studying enzyme mechanisms and designing potential drugs. Suicide substrates act as modified substrates for the target enzymes and bind to the active site. Therefore the presence of a competitive reversible inhibitor decreases the rate of substrate-induced inactivation and protects the enzyme from this inactivation. This lowering on the inactivation rate has evident physiological advantages, since it allows the easy acquisition of experimental data and facilitates kinetic data analysis by providing another variable (inhibitor concentration). However despite the importance of the simultaneous action of a suicide substrate and a competitive reversible inhibition, to date no corresponding kinetic analysis has been carried out. Therefore we present a general kinetic analysis of a Michaelis-Menten reaction mechanism with double inhibition caused by both, a suicide substrate and a competitive reversible inhibitor. We assume rapid equilibrium of the reversible reaction steps involved, while the time course equations for the reaction product have been derived with the assumption of a limiting enzyme. The goodness of the analytical solutions has been tested by comparison with the simulated curves obtained by numerical integration. A kinetic data analysis to determine the corresponding kinetic parameters from the time progress curve of the product is suggested. In conclusion, we present a complete kinetic analysis of an enzyme reaction mechanism as described above in an attempt to fill a gap in the theoretical treatment of this type of system.

Binding Sites↗

PubMed2002

Linear mixed irreversible inhibition of the autocatalytic activation of zymogens. Kinetic analysis checked by simulated progress curves.

Autocatalytic zymogen activation is a phenomenon of great importance for understanding some fundamental physiological processes involved in the enzyme regulation of gastrointestinal-tract enzymes, blood coagulation, fibrinolysis and the complement system. Examples of such processes are the activation of prekallikrein, trypsinogen and pepsinogen, all of which are controlled by natural proteinase inhibitors. This work studies the kinetics of a general autocatalytic zymogen activation process overlapped by two two-step irreversible inhibitions, i.e. a linear mixed irreversible inhibition. The kinetic equations for the whole course of the reaction are derived for this mechanism. In addition, we determine the corresponding kinetics for a number of particular cases of the general model analyzed, i.e. for reversible and irreversible non-competitive, competitive and uncompetitive inhibition systems which are considered particular cases of the general mechanism studied. The kinetic behavior of the system is related to a parameter, a dimensionless quantity, which shows whether the inhibition or the activation route prevails, in a similar way to that which we have previously carried out for other mechanisms. Finally, based on the kinetic equations obtained, a procedure for discriminating between the different mechanisms considered is suggested. The results of this contribution can be directly applied to most physiological autocatalytic zymogen activations in the presence of an inhibitor, allowing their complete kinetic characterization and suggesting procedures for varying the relative weight of the catalytic and inhibition routes or for changing the predominant route.

Algorithms↗

PubMed2002

Kinetics of alkaline phosphatase and lactoperoxidase inactivation, and of beta-lactoglobulin denaturation in milk with different fat content.

In the context of identifying intrinsic time temperature integrators (TTIs) for evaluating heat processing of milk, the extent to which milk fat content has an effect on alkaline phosphatase (ALP) and lactoperoxidase (Lpo) inactivation and on beta-lactoglobulin (beta-Ig) denaturation kinetics was studied. Inactivation and denaturation kinetics were analysed in whole, semi-skimmed and skimmed milk. In previous experiments (isothermal and non-isothermal heating conditions), heat inactivation of ALP and Lpo and heat denaturation of beta-Ig were found to follow first order kinetics. This allowed experimental design to be simplified. Data analysis was performed by non-linear regression and results were evaluated by construction of joint confidence regions. The possible effect of milk fat was illustrated by temperature time tolerance (TTT-) diagrams. Although initial ALP activity was lower in skimmed milk compared with semi-skimmed or whole milk, kinetics were comparable and fat content did not seem to substantially affect the ALP test result for pasteurized milk. Unlike ALP, Lpo inactivation and beta-Ig denaturation kinetics differed significantly in milk with different fat content. Differences between Lpo inactivation kinetics were relatively small and acceptable in the context of quantifying the process impact. Denaturation of beta-Ig, on the other hand, seemed to be enhanced at higher milk fat content (> 72 degrees C).

Alkaline Phosphatase↗