A theoretical discussion of the use of the Lineweaver–Burk plot to estimate kinetic parameters of intestinal transport in the presence of unstirred water layers

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Abstract
Transport of a solute molecule from the bulk phase in the intestinal lumen into the mucosal cells is determined by the rate of movement of the solute molecule across 2 barriers, the unstirred water layers (UWL) and the microvillus membrane. Failure to account for the effect of the resistance offered by the UWL introduces significant errors into the estimate of kinetic constants of carrier-mediated transport and these errors may be further magnified by the use of the Lineweaver-Burk plot. This study was undertaken to determine use of this plot under conditions that depict the effect of varying the effective resistance of the UWL, the distribution of transport sites along the villus (fn), the passive permeability coefficient (P), the maximal transport rate (Jdm) and the Km. Theoretical curves derived from a new equation demonstrate that the Lineweaver-Burk plot is linear under only a limited number of conditions and even then may lead to serious over- or under-estimation of Jdm and Km; failure to correct for passive permeation may give rise to additional quantitative discrepancies between the true and apparent values of Jdm and Km and the qualitative characteristics of a carrier-mediated intestinal transport system may be ascertained only after correction for the contribution of passive permeation and after correction for the effective resistance of the UWL.