Inhibition of cellular transport processes by 5-thio-d-glucopyranose

Abstract

5-Thio-d-glucopyranose, the nearest analogue of normal d-glucose, which is proving a useful tool in examinations of d-glucose biochemistry, affects active and facilitated-diffusion transport processes. 5-Thio-d-glucose is readily transported in rabbit kidney-cortex slices and reaches a tissue/medium ratio of 6.5 within 40min. The sulphur analogue shows typical saturation kinetics with a K_m value of 2.4mm and V_max. value of 70μmol/h per g of cell water. Uptake of 5-thio-d-glucose is phlorrhizin-sensitive, Na⁺-dependent and energy-dependent. d-Galactose and methyl α-d-glucopyranoside transport is competitively inhibited by 5-thio-d-glucose with K_i values of 4.8 and 9.7mm respectively. 5-Thio-d-glucose thus shows all of the characteristics of active transport in kidney cortex. Transport of neutral amino acids in rat kidney cortex is inhibited by 5-thio-d-glucose. Thus 5.6mm-5-thio-d-glucose causes a 25–30% inhibition of the transport of glycine and the non-metabolized amino acids cycloleucine and α-aminoisobutyric acid. 5-Thio-d-glucose is freely taken up by the facilitated-diffusion transport system in rat diaphragm muscle. The sulphur analogue inhibits the transport of d-xylose in this tissue but has no effect on the uptake of d-arabinose. It is concluded that the ring heteroatom is not an effector of binding in the transport processes examined and causes no important alteration in the conformation of the sugar. The diabetogenic action produced by 5-thio-d-glucose is due, in part, to the ability of the analogue to interfere with cellular transport processes that use d-glucose.