HIGH‐AFFINITY TRANSPORT AND PHOSPHORYLATION OF 2‐DEOXY‐d‐GLUCOSE IN SYNAPTOSOMES1,2

Abstract 2‐Deoxy‐ d ‐glucose (2 DG) entered synaptosomes (from rat brain) by a high‐affinity, Na + ‐independent glucose transport system with a K m , of 0.24 mM. 3‐O‐methyl‐glucose, D‐glucose, and phloretin were competitive inhibitors of 2‐DG transport with K i 's of 7 mM, 64 μM, and 0·75 μM, respectively. Insulin was without effect. 2‐DG uptake was also saturable at high substrate concentrations with an apparent low affinity K m , of 75 mM, where the K l , for glucose was 17.5 mM. We are not certain whether the rate‐limiting step for the low‐affinity uptake system is attributable to transport or phosphorylation. However, the high‐affinity glucose transport system probably is a special property of neuronal cell membranes and could be useful in helping to distinguish separated neurons from glial cells.