Citric-Acid-Cycle Intermediates and Other Anions

Compartmentation of Citric-Acid-Cycle Intermediates and Other Anions 

It is now well established that the compartmentation of whole segments of the citric acid cycle, between the mitochondria and the cytosol, is of major regulatory significance. In a later section of this chapter we will discuss the role of such systems in the control of major biosynthetic and biodegradative pathways. 

Electro genic. The translocation of anions results in an alteration of charge distribution across the inner mitochondrial membrane. An 

Electroneutral, proton compensated. The transport of pyruvate is accompanied by an exchange with hydroxyl ion but is equivalent to cotransport with protons, in which citrate plus a proton will translocate in exchange for malate, maintaining electroneutrality within the mitochondria. 

Electroneutral. This type of exchange is typified by the dicarboxylate shuttle. The basic requirement for anion shuttles of the type discussed above is the presence of an enzyme in the mitochondrial matrix and one in the cytosol, both of which catalyze the same reaction. 

---