Rejection criteria for the asymmetric carrier and their application to glucose transport in the human red blood cell

1. 1. We have derived two criteria, either of which is sufficient to permit the rejection of the conventional, asymmetric carrier model for facilitated diffusion for any given membrane transport system. These criteria involve only measurable parameters of transport. 2. 2. We have measured the half-saturation concentration of glucose at the inner face of the human red cell membrane at 20 °C using the infinite-cis procedure and found it to be 2.8 mM, with a standard deviation of 1.5 mM (eight observations). 3. 3. Using this result and previously determined experimental transport prameters, both of our rejection criteria force us to rule out the conventional, asymmetric carrier as a model for the glucose transport system of the human red blood cell. 4. 4. Our results are consistent with the tetramer model for sugar transport.