A method for conforming the pH dependence of the Michaelis parameters of nonallosteric enzymes to four kinetic schemes

Vega-Catalan, Fernando J.

doi:10.1016/0010-4809(90)90033-9

Cited by 4 publications

(2 citation statements)

References 6 publications

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“…As mentioned previously, it is known that the kinetic parameters of enzymes are sensitive to tem-perature, but they are also sensitive to pH (Vega-Catalan 1990). The enzyme and the substrate exist in many ionizable states, depending on the pH and the Michaelis parameters (K m and V max ), and thus uptake rates may vary with hydrogen ion concentration.…”

Section: Discussionmentioning

confidence: 99%

The Chemical Form of Dissolved Si Taken Up by Marine Diatoms

Amo

Brzezinski

1999

Journal of Phycology

121

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Resultsof past studies of the pH-dependent Si uptake kinetics of Phaeodactylum tricornutum Bohlin suggested that the anion SiO(OH) is the chemical Ϫ 3 form of dissolved Si taken up by marine diatoms. We determined the chemical form of Si taken up by three other marine diatom species and P. tricornutum by examining the kinetics of Si use under two dramatically different SiO(OH) :Si(OH) 4 ratios in sea-Ϫ 3 water by varying pH from ഠ8 to ഠ9.6. Uptake rates were determined using a precise and sensitive 32 Si tracer methodology. The pH-dependent uptake kinetics obtained for all species except P. tricornutum suggest that marine diatoms transport Si(OH) 4 . The half-saturation constant (K m ) varies strongly as a function of pH for all species when the substrate of transport is assumed to be SiO(OH) . Kinetic Ϫ 3 curves for Thalassiosira pseudonana (Hustedt) Hasle et Heimdal, Thalassiosira weissflogii (Grunow) G. Fryxell et Hasle, and Cylindrotheca fusiformis Reimann et Lewin have statistically identical values of K m at each pH when the substrate for transport is assumed to be Si(OH) 4 (T. pseudonana and T. weissflogii) or total dissolved silicon (C. fusiformis). In contrast, P. tricornutum exhibits unusual biphasic uptake kinetics: uptake conforms to Michaelis-Menten kinetics up to 15 to 25 M, above which uptake increases linearly. This enigmatic response may have biased conclusions drawn from past experiments using this species. However, based on the consistency of the results for the three other species, a new model of Si transport in marine diatoms is proposed on the basis of the direct formation of a complex between the Si-transport protein and Si(OH) 4 .

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Section: Discussionmentioning

confidence: 99%

The Chemical Form of Dissolved Si Taken Up by Marine Diatoms

Amo

Brzezinski

1999

Journal of Phycology

121

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“…The existing methods differ in the underlying mathematical principles, the amount of computational work needed, and the quality of the estimation (its accuracy and precision). In the very beginning of the computer era several programs were developed for calculating and V max on the mainframes in computer centres [ 9 - 19,20,23,32,33,36 ]. However, these programs have not been used widely because their application is accompanied with certain inconveniences.…”

Section: Introductionmentioning

confidence: 99%

A Computer Program for Processing Enzyme Kinetic Data by the Maximum Likelihood Method

Vaher¹

1995

Proceedings of the Estonian Academy of Sciences. Chemistry

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A personal computer complex program written in BASIC for the estimation of the Michaelis-Menten enzyme kinetics and inhibition constants or ligand binding process parameters and their confidence limits by the maximum likelihood method is presented. The program needs no provisional estimates of the constants for starting and is free from converging problems. To compare the method and the program with other methods (nonlinear regression by weighted least squares method and nonparametric "direct linear plot" developed by Cornish-Bowden), large-scale computer simulation experiments by the Monte Carlo method were performed. The results of these experiments demonstrate that the program works faster and provides the parameter estimates with less bias or variance. The listing of the program is presented.

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