The kinetics of selective biological transport. IV. Assessment of three carrier systems using the erythrocyte-monosaccharide transport data.

An assessment is made of the possible validity of three transport mechanisms proposed to describe the movement of monosaccharides in human erythrocytes. These mechanisms consist of a simple carrier system and two mechanisms derived from it, one of which postulates that the free carrier moves more slowly than the complexed carrier, and the other that slow diffusion steps occur at each surface of the membrane. None of these schemes provides an adequate quantitative description of the data so that all must be discarded, leaving the question of the mechanism still open to speculation.