Figure 2.

Eadie–Hofstee Plot of Initial Rate Radiotracer Amino Acid Influx Transport Kinetics.(A)Employing multivariate nonlinear analyses of zero-trans unidirectional [³H]-l-alanine initial influx rates measured in reconstituted lyophilized intestinal BBMVs, a single linear component B⁰AT1 (black circles) was derived by subtracting simple passive diffusion (blue triangles) from total l-alanine uptake in Na⁺ media. The B⁰AT1 component fit saturable kinetics per eqn (1) (see the Methods section), defining >95% of the Na⁺-dependent carrier-mediated uptake, as represented by the solid line within green 95% CI. The computed passive diffusion permeability coefficient, P, of eqn (1) (abscissa intercept of vertical dashed line) was also independently empirically verified by measuring uptake in K⁺ media replacing Na⁺ in the presence of 100 mml-alanine and/or 100 mm unlabeled methionine. (B) An apparent additional trivial carrier-mediated component, labeled “Other” (red open circles), contributed <5% of total Na⁺-dependent maximum uptake activity, and was dropped from subsequent considerations.