Transport of hexoses in yeast. Re-examination of the sugar phosphorylation hypothesis with a new experimental approach.

The constitutive transport of hexoses in yeast has been re-examined with a new radioactive experimental approach devised to distinguish between association or independence of the transport step with phosphorylation of the sugar substrate. The approach takes advantage of the fact that the label of [2-3H]mannose disappears once it has been phosphorylated by the yeast, due to its conversion to fructose-6-phosphate. Our results with wild-type yeast and this fermentable sugar support the view that the transport of hexoses in yeast does not involve phosphorylation of the substrate. Other features of the transport process have been examined using this experimental procedure and are also reported.