The absorption of glucose by Scenedesmus quadricauda I. Some kinetic aspects

The effect of various conditions on the rate of uptake of glucose by the green alga Scenedesmus quadricauda has been examined. With cells starved by keeping for at least 24 h in the dark, the concentration/rate curve reaches a maximum at 2% glucose, when the rate is 4 x 10–13 gmol min–1 μ–2. With fresh cells the same maximum rate is achieved at the same concentration, but the form of the curve is different. Between 0.1 and 0.5% glucose there is a constant rate of uptake which is only half that of the maximum value. In all cases the progress curve of glucose uptake is linear with respect to time. Increase of the exposed area of the plasma membrane by plasmolysis gave a barely significant increase in the rate of glucose uptake. It was therefore concluded that glucose absorption did not take place over the whole surface of the plasma membrane, but only at specific absorption centres, and that the uptake was not limited by thermal diffusion.