Transporters adenine nucleotide translocase

Figure 9.19 Adenine nucleotide translocase and phosphate transfer into the matrix. Phosphate is transported into the mitochondria with protons in a symport transport system. The adenine nucleotide translocase transports ADP into and ATP out of the mitochondria, i.e. it is electrogenic. The charge is neutralised by H movement into the matrix from the proton motive force which utilises about 25% of the energy in the proton motive force.

The adenine nucleotide translocase, integral to the inner membrane, binds ADP3 - in the intermembrane space and transports it into the matrix in exchange for an ATP4 molecule simultaneously transported outward (see Fig. 13-1 for the ionic forms of ATP and ADP). Because this antiporter moves four negative charges out for every three moved in, its activity is favored by the... 

Figure 7.4 Cartoon of transport reaction catalyzed by adenine nucleotide translocase (ANT). ATP4- in the mitochondrial matrix is exchanged for ADP3- in intermembrane space between the outer and inner mitochondrial membranes.

As discussed in Section 7.2.2, ATP is delivered to the intermembrane space via the adenine nucleotide translocase (ANT) enzyme. The reference transport reaction is... 

Mitochondria and cell death Although oxidative phosphorylation is a mitochondrial process, most ATP utilization occurs outside of the mitochondrion. ATP synthesized from oxidative phosphorylation is actively transported from the matrix to the intermembrane space by adenine nucleotide translocase (ANT). Porins form voltage-dependent anion channels (VDAC) through the outer mitochondrial membrane for the diffusion of H2O, ATP metabolites, and other ions. Under certain types of stress, ANT, VDAC, and other proteins form a nonspecific open channel known as the mitochondrial permeability transition pore. This pore is associated with events that lead rapidly to necrotic cell death. 

Fig. 21.13. Transport of compounds across the inner and outer mitochondrial membranes. The electrochemical potential gradient drives the transport of ions across the inner mitochondrial membrane on specific translocases. Each translocase is composed of specific membrane-spanning helices that bind only specific compounds (ANT adenine nucleotide translocase). In contrast, the outer membrane contains relatively large unspecific pores called VDAC (voltage-dependent anion channels) through which a wide range of ions diffuse. These bind cytosolic proteins such as hexokinase (HK), which enables HK to have access to newly exported ATP.

The adenine nucleotide carrier or translocase is specifically inhibited by atractyloside (competitive with respect to adenine nucleotide) and bongkrekic acid (noncompetitive). Atractyloside has been known for some time to be highly poisonous and its mechanism of action attests to the importance of the adenine nucleotide translocase. Other nucleotides, such as GTP, must first be converted to ATP by nucleoside diphosphokinase prior to transport out of the mitochondria. The outer mitochondrial compartment also contains nucleoside diphosphokinase for the conversion of ATP to GTP. 

The adenine nucleotide transporter is known as a translocase - it transports ADP into and ATP out of the mitochondrion in such a way that, when one molecule of ADP is transported in, one molecule of ATP is transported out... 

The major function of oxidative phosphorylation is to generate ATP from ADP. However, ATP and ADP do not diffuse freely across the inner mitochondrial membrane. How are these highly charged molecules moved across the inner membrane into the cytosol A specific transport ATP-ADP translocase (also called adenine nucleotide... 

---