Sugar Transport in Neurospora crassa

Abstract

1 Uptake of [14C]sorbose and 3-O-[14C]methylglucose into ungerminated and germinated conidia as well as mycelia of Neurospora crassa was determined by means of the millipore filter technique. 2 The rate of uptake of both sugars is lower in glucose-germinated conidia than in ungerminated conidia (glucose-repression). In germinated conidia it increases upon their starvation in mineral salts solution (derepression), in ungerminated conidia it remains constant. 3 Both in ungerminated conidia and in starved, glucose-germinated conidia, the rate of uptake of both sugars is maximal at pH 4.75. This would suggest that the transport systems measured are identical. However, Km-measurements revealed two separate systems for sorbose uptake in the two different cell types (Km ungerminated: 3.5 mM, Km germinated and starved: 10 mM), and one single system for 3-O-methylglucose uptake (Km 0.03 mM).