Uptake ofd-Glucosamine bySaccharomyces cerevisiae

d-glucosamine does not serve as a metabolic substrate inSaccharomyces cerevisiae although it stimulates by 15% endogenous respiration. It is taken up by a system or systems shared withd-glucose,d-fructose andd-xylose but apparently not fully with 2-deoxy-d-glucose. Its half-saturation constant is 38±14 mmol/L, in agreement with its inhibitor constant versusd-glucose andd-xylose uptake. Its maximum rate is 69±17 μmol per g dry mass per min. The transport is thermodynamically passive butd-glucosamine distribution follows the membrane potential, reaching ratios of 80∶1 at pH 7.5 and about 1∶1 at pH 4.0. These rations decrease with increasingd-glucosamine concentration as well as with increasing suspension density, and are affected by metabolic inhibitors.