Measurement of sugar transport in ejaculated bovine sperm is complicated by a small intracellular volume and a rapid rate of sugar uptake. However, initial rates of sugar uptake can be obtained using 2-deoxyglucose as a model substrate. Accumulation of 2-deoxyglucose involves both transport and phosphorylation and can be monitored accurately by measuring only intracellular 2-deoxyglucose-6-phosphate. Uptake of 2-deoxyglucose was linear for 10 seconds at 22°C and followed simple Michaelis-Menten kinetics with a Km of 0.2 mM and a Vmax of 2 µmole/h/108 cells. Phloretin was a competitive and cytochalasin B a noncompetitive inhibitor of 2-deoxyglucose uptake and since neither compound inhibited hexokinase, transport is the rate determining step in the uptake of 2-deoxyglucose. Comparison of the inhibition kinetics of 2-deoxyglucose uptake and of sperm hexokinase using several sugars also supports this conclusion. The accumulation of 2-deoxyglucose-6-phosphate within the cell is probably regulated by several factors, such as the activity of hexokinase, the level of ATP, inhibition of hexokinase by 2-deoxyglucose-6-phosphate and the activity of a hexose-6-phosphate phosphatase. These combine to control the steady state levels of 2-deoxyglucose-6-phosphate within the cell and limit total accumulation to about 30 nmole/108 cells.
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Hiipakka et al. (1978) studied this question.