Intestinal transport of amino acids and sugars: advances using membrane vesicles

Glucose crosses the intestinal brush border via one diffusive and two saturable systems. Under zero-trans conditions, the major saturable system has the characteristics of an Iso Ordered Bireactant system with one Na binding and, additionally, shows the properties of trans inhibition by Na and sensitivity to Em. An additional high-affinity saturable system exists with a Kt in the micromolar range and has the capacity for binding multiple Na+ ions. Biochemical and transport studies indicate that the brush-border Na-glucose cotransporter may be asymmetric with respect to the inner and outer membrane face. The Na-independent glucose carrier found in enterocyte basolateral membranes strongly resembles the facilitated glucose carrier found in other membranes.