How a soluble enzyme can be forced to work as a transport system: description of an experimental design.

The cellular transport systems which have been studied up to now have been found to be based on the functioning of specialized proteins anchored asymmetrically in cell membranes. In the present paper we show that a single soluble enzyme inserted at random in a gel slab can drive an uphill transport, provided that asymmetrical boundary conditions force the reversible reaction catalyzed by this enzyme to work forward on one face of the gel slab and backward on the other face. Experimentally, we have used a yeast alcohol dehydrogenase to induce an uphill transport of NADH. It cannot be excluded that comparable structurally symmetrical transport systems also exist in living cells. Such systems would be particularly well suited to preserving cell homeostasis with regard to small solutes.