Sugar Transport in Neurospora crassa*

The transport of several sugars by cells of Neurospora crassa grown in shake culture has been investigated. 3-OMethyl-n-glucose is a substrate for the glucose transport system in glucose-grown cells but cannot be phosphorylated by the ATP-dependent hexokinase which readily catalyzes the phosphorylation of D-glucose. Since this nonmetabolizable glucose analogue cannot be accumulated against a concentration gradient in cells grown on glucose, it appears that net glucose uptake in glucose-grown cells involves a facilitated diffusion transport step followed by ATP-dependent phosphorylation and subsequent metabolism of the transported glucose. Growth of cells on D-fructose leads to the appearance of a system which catalyzes the accumulation of unaltered 3-O-methyl-D-glucose and L-sorbose against considerable concentration gradients.