Current trends in the estimation of Michaelis-Menten parameters

Atkins, Gordon L.; Nimmo, Ian A.

doi:10.1016/0003-2697(80)90268-7

Cited by 106 publications

(53 citation statements)

References 34 publications

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“…Analysis by the double reciprocal (Lineweaver-Burk) method (17), as well as single reciprocal methods (Hanes and Eadie-Hofstee, and their reciprocals [18]) found MichaelisMenten equations and curves inconsistent with the observed data. Because these reciprocal methods can be inaccurate and/ or imprecise (18), computerized nonlinear least squares regression analysis (18)(19)(20)(21)(22) was used to find the Michaelis-Menten equation that best fit the data in terms of the lowest mean squared error (software was from SAS Institute, Inc., Cary, NC). The resultant equation (and curve), however, was also inconsistent with the data.…”

Section: Resultsmentioning

confidence: 99%

Intestinal absorption of magnesium from food and supplements.

Fine¹,

Ana²,

Porter³

et al. 1991

J. Clin. Invest.

258

152

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The purpose of this study was to measure magnesium absorption over the wide range of intakes to which the intestine may be exposed from food and/or magnesium-containing medications. Net magnesium absorption was measured in normal subjects after they ingested a standard meal supplemented with 0, 10, 20, 40, and 80 mEq of magnesium acetate. Although absorption increased with each increment in intake, fractional magnesium absorption fell progressively (from 65% at the lowest to 11% at the highest intake) so that absorption as a function of intake was curvilinear. This absorption-intake relationship was almost perfectly represented by an equation containing a hyperbolic function plus a linear function. Our results are statistically compatible with a magnesium absorption process that simultaneously uses a mechanism that reaches an absorptive maximum, plus a mechanism that endlessly absorbs a defined fraction (7%) of ingested magnesium. Compared to previous studies of calcium absorption, much less magnesium than calcium was absorbed at intakes above 8 mEq/meal, apparently due to greater restriction of intestinal permeability to magnesium. We also found that magnesium from a high magnesiumcontaining food source, almonds, was just as bioavailable as from soluble magnesium acetate. In contrast, magnesium absorption from commercially available enteric-coated magnesium chloride was much less than from magnesium acetate, suggesting that enteric coating can impair magnesium bioavailability. (J. Clin. Invest. 1991.88:396-402.)

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Section: Resultsmentioning

confidence: 99%

Intestinal absorption of magnesium from food and supplements.

Fine¹,

Ana²,

Porter³

et al. 1991

J. Clin. Invest.

258

152

View full text Add to dashboard Cite

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“…For a model with a saturable and a non saturable component, weighted nonlinear regression is su perior to graphical methods and most nonparametric procedures fo r the determina tion of V max ' Km, and Kd (C unningham and Sarna, 1979;Atkins and Nimmo, 1980;Atkins, 1983).…”

Section: Discussionmentioning

confidence: 99%

“…Regressi on analysis, however, requires appro priate weighting when there is inhomogeneity of variance in the data (Atkins and Nimmo, 1980;Draper and Smith, 1981). Although nonlinear regression has been used to determine the V max and Km of cerebrovascular LNAA transport, adequate weighting of the data was not employed in these studies (Pardridge and Oldendorf, 1975;Daniel et aI., 1977;Pardridge and Mietus, 1982), even though there is significant inhomogeneity of variance in PA, l in ' and BUI data (C unningham and Sarna, 1979; see also Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Weighting factors were taken as the inverse square of the SD of leucine influx or of PA. Because five or more replicates are necessary to obtain a good experimental estimate of the SD (Atkins and Nimmo, 1980), the SD at each perfusate concentration was calculated as follows from the magnitude of PA or lin' For the simplest weighting function, the SD was taken as proportional to the PA or lin value. To more accurately describe the re lation between the SD and the mean PA or lin value, the following equations were fitted by linear least squares to the PA or lin data, where a, b, d, f, and g are constants and X is the mean regional P A or lin at a specific perfusate leucine concentration:…”

Section: Kinetic Analysismentioning

confidence: 99%

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Regional Cerebrovascular Transport of Leucine as Measured by the in situ Brain Perfusion Technique

Smith

Takasato

Sweeney

et al. 1985

J Cereb Blood Flow Metab

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Summary: Leucine influx into six brain regions was de termined in anesthetized rats with the in situ brain per fusion technique using either saline or plasma perfusate.This technique has several advantages over other methods such as the brain uptake index (BUI) technique.The concentration dependence of L-Ieucine influx was best described by a model with a saturable and a nonsat urable component. For the saturable component, Villa, equaled 10,67 ± 0.21 x 10-4 fLmol S-l g I and Kill equaled 0.0257 ± 0.0009 fLmol ml-I, whereas the con stant of non saturable diffusion (Kd) equaled 0.957 ± 0.067 x 10-4 S -I in the parietal lobe during saline per fusion. V rna' was higher in the cortical lobes than in other brain areas, probably owing to a greater capillary surface area. There were no regional differences in Kill or Kd. The apparent Kill for L-Ieucine during plasma perfusion wasThe cerebrovascular endothelium. in addition to restricting the exchange of ions. proteins, and hy drophilic nonelectrolytes, has specific transport systems for rapid transfer of essential nutrients from plasma to brain (Rapoport, 1976 port (Takasato et aI., [984). First, the perfusion technique is 100 times more sensitive than the BU[ technique for the measurement of cerebrovascular permeability. Second, the rat� 01' regional cerebral perfusion is measured directly during perfusion, whereas the cerebral flow rate of the B UI intraca rotid bolus has never been determined experimen tally. Third, with the perfusion technique, there is negligible mixing of perfusate with blood before the perfusion fluid reaches the brain capillaries (Taka sato et aI., [984). In contrast, the assumption that the B U [ intracarotid bolus does not mix with blood before reaching the capillaries has never been ver ified experimentally (Fenstermacher et aI., 198 I).Minimal mixing is important, owing to the sensi tivity of cerebrovascular amino acid transport to competition effects (Rapoport, [976; Pard ridge . 1977a). Fourth, the perfusion technique, unlike the intravenous injection method, allows virtually ab solute control of solute concentrations in brain cap illaries. And last, the perfusion method, unlike the intravenous injection method, is not subject to er-

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“…Es ist im allgemeinen nicht zulässig, die Gesamtmenge des Kpmpetitof s im Reaktionsansatz der Konzentration des "freien" Kofhpetitors gleichzusetzen, wie es im allgemeinen in der Enzymkuietik üblich ist, z.B. bei der Meßwertverarbeitung imDötön-piagramm (1,8). Da aber andererseits die Auswertung der Funktion B = f(T) auf größere Schwierigkeiten stoßen kann als die Auswertung der Scatchard-funktion, wird vorgeschlagen, die Meßwerte zunächst im Diagramm B = f (T) anzuordnen und die dadurch ermittelten Funktiönswefte in dasScafc/wrrf-Diagramm B/F = f(B) zur endgültigen Auswertung einzutragen (l , 9).…”

Section: Meßwertverarbeitungunclassified

Kritische Anmerkungen zur Auswertung von Rezeptoranalysen

Kuß¹

1982

CCLM

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Critical comments on the calcülation ofreceptor analysesSummary: The main literature concerning the processing of binding data is reviewed. Practical conclusions for the measurement of association constants and binding stte concentrations are considered from the standpoint of basic binding theory in connection with basic Information theory. The theoretical minimum errors in the association constant and the binding site concentration are discussed äs ä funetion of the Saturation fraction of the most dilute component. Various plotting forms and the error arising from various rearrangements of the basic binding equation are discussed. For fitting procedure several heuristic modeis are mentioned and it is recömmended to Start from the most geriefvlAdäir funetion. The necessity of well defined criteria for quality of fit in Computer programming for iterative curve fitting procedures is emphasized. The most frequent, however avpidable, errors are mentioned. EinführungDie Liganden werden zumeist in leicht meßbarer Form Rezeptoranalysen gehören zu den Titrationsverfahren * s >£ifi<*e" Verbindungen, häufig als radioaktive der analytischen'^«. Die einfachsten Beispiele werVerbindungen mit bekannter spezifischer Aktmtat den idealisiert wie folgt beschrieben: Der eine Reaktions-(Bq/mol), eingesetzt. Deren als Meßgroßen herangezoteünehmer Q ("Binder", "Rezeptor") mit der unbekaftn-««· Konzentrationen werden ggf. in Analogie zu Gl. la

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Current trends in the estimation of Michaelis-Menten parameters

Cited by 106 publications

References 34 publications

Intestinal absorption of magnesium from food and supplements.

Intestinal absorption of magnesium from food and supplements.

Regional Cerebrovascular Transport of Leucine as Measured by the in situ Brain Perfusion Technique

Kritische Anmerkungen zur Auswertung von Rezeptoranalysen

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