USE OF GLUCOSE-TRANSPORT MUTANTS TO EXAMINE THE INTRINSIC-PROPERTIES OF GLUCOSE-TRANSPORT PROCESSES IN RAT MYOBLASTS

Glucose transport mutants were used to examine the intrinsic propertie s of glucose transport processes in rat myoblasts. Studies with mutant s devoid of any functional glucose transporter revealed that substanti al amount of sugar analogues was internalized via simple diffusion; ho wever, equilibration of these analogues across the plasma membrane was not achieved after 1 min of incubation at 23 degrees C. The rates of internalization were substantially higher with sugar analogues that we re phosphorylated by intracellular kinases. Mutants harbouring only on e functional GLUT transporter were also used to examine the intrinsic properties of specific GLUT transporters. The preferred substrate for the GLUT 1 transporter was 2-deoxy-D-glucose (dGlc); the transport aff inity for this substrate was reduced by energy uncouplers. Studies wit h mutants possessing only the GLUT 4 transporter revealed that this tr ansporter existed in a high and a low affinity form. The former was re sponsible for dGlc uptake; whereas the latter was for the uptake of bo th 3-O-methyl-D-glucose (MeGlc) and dGlc; only the former was affected by energy uncouplers. These studies illustrated the usefulness of mut ants in characterizing glucose transport processes.