Radiation-inactivation analysis of the oligomeric structure of the renal sodium/d-glucose symporter

Abstract

AbstractThe radiation-inactivation size (RIS) of the rat renal brush-border membrane sodium/d-glucose cotransporter was estimated from the loss of transport activity in irradiated membrane vesicles. The RIS depended on the electrochemical conditions present when measuring transport activity. A RIS of 294±40 kDa was obtained when transport was measured in the presence of a sodium electrochemical gradient. Under sodium equilibrium conditions, the RIS was 84±25 kDa in the presence of a glucose gradient, and 92±20 kDa in its absence. In the absence of a sodium gradient, but in the presence of an electrical potential gradient, the RIS increased to 225±49 kDa. The 294 kDa result supports earlier suggestions that the Na+ gradient-dependent glucose transport activity is mediated by a tetramer. Individual monomers appear, however, to carry out glucose transport under equilibrium exchange conditions or when a glucose gradient serves as the only driving force. The electrical potential gradient-driven glucose transport RIS appears to involve three functional subunits