Respiratory increase and active hexose uptake of Chlorella vulgaris

Abstract

1. 1. When non-metabolizable glucose analogues like 3- O-methylglucos and 6-deoxyglucose are added to Chlorella vulgaris cells an increase in the rate of respiration is observed. 2. 2. This respiratory increase is strictly correlated with sugar transport since (a) non-induced cells do not respond to the addition of sugars; (b) only transportable sugars cause the respiratory increase; (c) the extent of the increase in O 2 uptake depends on the amount of sugar added, whereby the different K m values for uptake of various sugars correspond closely to the “ K m values” for the increased O 2 uptake. 3. 3. Each extra O 2 brings about the uptake of 5.1 molecules of 6-deoxyglucose, which corresponds to 1.18 “ATP” per sugar. For glucose, which is rapidly metabolized in the cells, this ratio is 2.5 ATP per glucose taken up. The extra ATP covers exactly the energy required for the conversion to sucrose and starch of most of the glucose taken up. 4. 4. In the presence of 6-deoxyglucose the increased respiration is the same during steady state (net influx being zero) as at the onset of sugar uptake. Since the influx during steady state is about twice the initial influx (positive transmembrane effect) the ratio “ATP” required per 6-deoxyglucose taken up decreases during uptake and reaches 0.5 to 0.6 during steady state. 5. 5. Steady-state influx is completely energy dependent; it can be fully inhibited by uncoupling agents. It is considerably less sensitive, however, to sodium azide than net influx. These and the above observations (see 4) can be explained by assuming that during steady-state part of the transport energy required is supplied by respiration and part by a direct reversal of the influx reaction; uncouplers inhibit both kinds of energy generation. 6. 6. All data reported are compatible with the model presented in the preceding publication.