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Figure
10. Work in the form of DpH or
DY is required for active
transport. The experiments shown are typical flow dialysis experiments
as described in Fig. 7, except that valinomycin has been added prior to [14C]acetate,
so that DpH is the only component
of
 present.
As previously, when ASC/PMS is added, [14C]acetate is
accumulated, and its concentration in the dialysate decreases dramatically.
When a new equilibrium is reached, lactose is added to the upper chamber
containing membrane vesicles that contain the lactose permease (·
in A). About half of the accumulated weak acid is rapidly released,
indicating that lactose accumulation occurs at the expense of
DpH. The remaining weak acid is
then released by nigericin. When membrane vesicles without the lactose
permease are used (o), nothing happens when
lactose is added. In panel B, a similar experiment is shown for
glucose-6-phosphate accumulation in vesicles that contain a permease
specific for this substrate.
When the converse experiment is carried out with TPP+ (with
nigericin added first so that DY is
the sole component of
),
the same type of phenomena are observed.
Therefore, it is apparent that in order for the vesicles to accumulate
lactose or glucose-6-P, energy is expended in the form of either
DpH
or DY.
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