ADP/ATP transporter

Cavalier-Smith T (1987b) Eukaryotes with no mitochondria. Nature 326 332-333 Chan KW, Slotboom DJ, Cox S, Embley TM, Fabre O, van der Giezen M, Harding M, Horner DS, Kunji ERS, Leon-Avila G, Tovar J (2005) A novel ADP/ATP transporter in the mitosome of the microaerophilic human parasite Entamoeba histolytica. Curr Biol 15 737-742... 

Functional Differences Between Mitochondrial and Alternative ADP/ATP Transporters... 

Although remarkable progress has been made in matching the secondary structure and the function in the various members of the mitochondrial carrier family (del Arco and Satrustegui 2005), satisfying information about the function of potential ADP/ATP transporters can only come from a detailed functional analysis (see later). Several methods are currently available reconstitution in liposomes, in vivo expression, rescue experiments, and functional tests in bacteria (Escherichia coli, Lactococcus lactis). Such tests involve competition experiments, effector and inhibitor studies (Voncken 2001 Voncken et al. 2002a Haferkamp et al. 2002 van der Giezen et al. 2002 Tjaden et al. 2004 Chan et al. 2005 Leroch 2006). 

Table 7.1 shows that one mitochondrial, two hydrogenosomal, and one mitosomal ADP/ATP transporter all possess different Km values and have different requirements for a membrane potential. Also, the spectrum of nucleotides which can be transported by the various proteins is quite peculiar at present, the transporter of Entamoeba is the only ADP/ATP transporter that also transports AMP, just like its relative (brittle-1) in the plastids of Solanum tuberosum (Leroch et al. 2005 Table 7.2). In addition, the different ADP/ATP transporters exhibit a peculiar spectrum of sensitivity, or resistance,...

In the previous section we mentioned the ADP/ATP transporter, and it is also shown in Figure 17.2. This system allows the export of ATP and import of ADP. Because ATP and ADP have net charges of -4 and -3, respectively, at pH 7, the transport is not electroneutral and must occur at the expense of the membrane potential. Atractyloside and bongkrekic acid are inhibitors of this system, the former binding to the ADP binding site of the porter and the latter to the ATP site. Associated with ADP/ATP transport is the transport of P which must enter the mitochondrion to participate in ATP formation. Several systems for transport-... 

Klingenberg, M. (1980). The ADP-ATP translocation in mitochondria, a membrane potential controlled transport. J. Memb. Biol. 56, 97-105. 

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... 

Peter Mitchell (Nobel Prize, 1978) of Great Britain was the first to realize, and to propose in his chemi-osmotic theory, that the energy required for die ADP-ATP reaction could be derived by an accretion of protons in the thylakoid sac to the point at which the electrochemical gradient across the membrane could effect the proton transport required as die driving force for this reaction. See also Phosphorylation (Photosynthetic). 

Rivera MC, Jain R, Moore JE, Lake JA (1998) Genomic evidence for two functionally distinct gene classes. Proc Natl Acad Sci USA 95 6239-6244 Saraste M, Walker JE (1982) Internal sequence repeats and the path of polypeptide in mitochondrial adp/atp translocase. FEBS Lett 144 250-254 Schatz G (1998) Protein transport - the doors to organelles. Nature 395 439-440 Schatz G, Haslbrunner E, Tuppy H (1964) Deoxyribonucleic acid associated with yeast mitochondria. Biochem Biophys Res Commun 15 127-132 Schimper AFW (1883) Ober die Entwicklung der Chlorophyll Kijrner und Farbkorner. Bot Zeit 41 105-114... 

Fig. 7.4. Phylogenetic analysis of the ADP/ATP carriers (AACs) has so far revealed that only the hydrogenosomes of chytrids and ciliates possess genuine mitochondrial AACs, which cluster with the mitochondrial homologues of their aerobic, mitochondria-bearing relatives (2, 3) (Voncken 2001 Voncken et al. 2002a van der Giezen et al. 2002 Tjaden et al. 2004). The AAC of the mitochondrial remnant of Cryptosporidium clusters with the mitochondrial transporters of the distantly related Plasmodium (the closest relative from which a complete genome DNA sequence is available) (1). Trichomonas (5) and Entamoeba (4) use alternative members of the mitochondrial carrier family for the transport of ATP across the hydrogenosomal/mitosomal membranes (Dyall et al. 2000 Tjaden et al. 2004 Chan et al. 2005 Tjaden and Leroch, unpublished results)...

ADP phosphorylation is tightly coupled to electron transport. Shutting down one shuts down the other. It is well known that if ADP phosphorylation is inhibited by such compounds as oligomycin, electron transport also ceases. If the proton gradient is broken by a proton ionophore, however, such as 2,4-dinitrophenol, electron transport resumes at a rapid pace and no phosphorylation takes place. Such proton ionophores are also termed "uncouplers" of electron transport and ADP phosphorylation. Under normal conditions, the factors limiting ATP production are the pH gradient across the inner mitochondrial membrane and the cellular ADP/ATP ratio. An increase in the proton gradient shuts down phosphorylation and electron transport, whereas an increase in the ADP/ATP ratio stimulates both. Stimulation of oxidative phosphorylation by increases in cellular ADP concentration is termed respiratory control. 

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