Specificity of sugar transport across the brush border of the rat proximal tubule.

By chemical and electrical measurements the transport of 25 sugars in the proximal tubule of the rat kidney was investigated. The data gained reveal the following structural requirements for the D-glucose transport system in the renal brush border: A free OH in the D-gluco-configuration on C atom 2 is most important - OH in equatorial position of the chair Cl conformation -. A free OH on C-3 in the equatorial configuration is also essential. If the OH on C-4 turns from the equatorial to the axial configuration the transport is 50% reduced. The OH on C-6 may be missing if otherwise the D-glucose configuration is unchanged. But if in addition the position of OH in C-4 has changed the transport ceases. Furthermore the presence of a C-6 atom and of a ring structure is necessary.