The metabolism of sorbitol and fructose by ram spermatozoa has been examined under both aerobic and anaerobic conditions. Isotopically labelled substrates were used to measure substrate oxidation under aerobic conditions or substrate dismutation under anaerobic conditions.
In combination, fructose was used preferentially and, when little or no sorbitol was present at the beginning of incubation, some of the fructose disappearing accumulated as the polyol. The remaining fructose utilized, but not oxidized or dismutated, was quantitatively converted to lactate. When sorbitol was the only substrate in the diluent, it was not utilized under anaerobic conditions and a large part of the sorbitol utilized under aerobic conditions was oxidized. Under the latter conditions, the rate of utilization of the polyol was related to its concentration. It appears that this substrate is made available to the cell by passive diffusion and that this process plays a part in limiting the availability of sorbitol to the cell.
The addition of 10-4m 2 : 4 dinitrophenol increased oxygen uptake and substrate oxidation when fructose was present in the diluent. With sorbitol as substrate, dinitrophenol decreased substrate oxidation. Under anaerobic conditions, dinitrophenol decreased both sorbitol accumulation from fructose and dismutation of fructose. It is suggested that the dismutation reaction may be linked with the reduction of fructose to sorbitol to balance nad : nadh ratios.
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