Although the overall processes of photosynthesis and mitochondrial oxidation are well understood, many important details remain to be uncovered by a new generation of scientists. For example, little is known about how complexes I and IV in mitochondria couple proton and electron movements to create a proton-motive force. Similarly, although the binding-change mechanism for ATP synthesis by the FqFj complex is now generally accepted, we do not understand how conformational changes in each ß subunit are coupled to the cyclical binding of ADP and P(, formation of ATP, and then release of ATP. Many questions also remain about the structure and function of transport proteins in the inner mi-tochondrial and chloroplast membranes that play key roles in oxidative phosphorylation and photosynthesis. Molecular analysis of such membrane proteins is difficult, and new types of techniques will be needed to elucidate the details of their structure and operation.
We now know that release of cytochrome c and other proteins from the intermembrane space of mitochondria into the cytosol plays a major role in triggering apoptosis (Chapter 22). Certain members of the Bcl-2 family of apoptotic proteins and ion channels localized in part to the outer mitochondrial membrane participate in this process. Yet much remains to be learned about the structure of these proteins in the mitochondrial membrane, their normal functions in cell metabolism, and the alterations that lead to apoptosis.
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