Optical methods for measuring protein-protein interactions.

The hepatopancreas protein, therefore, probably represents the membranous proton channel of the vacuolar ATPase and electron microscopy has given us the clearest impression yet of its organization; an organization clearly consistent with the functional characteristics of the chloroplast ATPase-CF,, complex [22]. It is hoped that techniques such as electron diffraction may improve the structural resolution obtained. The intriguing question which now arises is the mechanism by which specific unidirectional proton transport is achieved. Clearly, the central channel does not possess a sufficient degree of discrimination. This will most probably be conferred on the system by the additional water-soluble subunits which make up the whole molecular assembly. By analogy with the mitochondria1 ATPase, where DCCD effectively blocks proton transport, it may be that initial uptake by the membrane involves the region between the four helices which constitute the individual subunit. Whatever process occurs, it is clear that the 16 kDa protein presents us with an advantageous system through which the principles of membrane protein structure and assembly can be investigated.