ABSTRACT
We are now entering a period of “ moving pictures” , in which we can actually see the protein machinery at work; MgATPase functions as a rotary motor, the Bi2dependent mutase as a reciprocating nutcracker or jaw-crusher. For many bioche mists, conformation changes remain associated primarily with allosteric proteins or relegated to a supporting role in enzymes (e.g. binding the substrate or control by an allosteric effector) rather than being accorded a direct role in the reaction mechanism. The MgATPases and Bi2-dependent mutases provide examples of enzymes that use conformation changes to drive the reaction (in the former) or drastically change the properties of the active site (in the latter) and highlight the importance of conforma tion changes and energy transduction for metalloenzyme activity. They complement better known examples of conformation changes in, for example, the allosteric hemo globins (Chapter 9) and pyruvate kinase (Chapter 8) and the Ca-binding signaling proteins (Chapter 5). For many researchers the direct observation of rotation of the central shaft of MgATPase served to announce that the concept of protein engines and machines had emerged from the realms of science fiction into reality. This should encourage a more dynamic view of the functioning of metalloenzymes and proteins (Sec. 2.3).
