Adenine nucleotide carrier

Joseph-Iiauzun, E., Farges, R., Delmas, P., Ferrara, P. Loison, G. (1997). The Mr 18,000 subunit of the peripheral-type benzodiazepine receptor exhibits both benzodiazepine and isoquinoline carboxamide binding sites in the absence of the voltage-dependent anion channel or of the adenine nucleotide carrier. J. Biol. Chem. 272, 28102-6. 

McEnery, M.W., Snowman, A.M., Trifiletti, R.R., and Snyder, S.H., 1992, Isolation ofthe mitochondrial benzodiazepine receptor association with the voltage-dependent anion channel and the adenine nucleotide carrier, Proc.Natl.Acad.Sci. U.S.A. 89 3170-3174. 

Tire important adenine nucleotide carrier takes ADP into the mitochondrial matrix for phosphorylation in a 1 1 ratio with ATP that is exported into the cytoplasm.299 300b This is one of the major rate-determining processes in respiration. It has been widely accepted that the carrier is electrogenic,300... 

Table 7.1. Km values for ADP and ATP of several heterologously expressed adenine nucleotide carriers determined on intact Escherichia coli cells under various energy conditions (coupled and uncoupled). Km is given in nanomoles per milligram of protein per hour), E. coli cells were preincubated with 100 pM carbonyl cyanide 3-chlorophenylhydrazone (CCCP) for 2 min for uncoupling. Uptake studies were performed as described in Haferkamp et al. (2002), Tjaden et al. (2004) Leroch (2006), and Leroch et al. (2005)...

Table 7.2. Effects of various metabolites on [a32P]ADP uptake into E. coli cells expressing several adenine nucleotide carriers. For uptake experiments, effectors were always present in a fivefold higher concentration than the given uptake substrates. [a32P]ADP uptake by AAC2(A.t.), AACl(N.sp.), HMP31(T.g.), and ANTl( ./z.) was measured at a substrate concentration of 10, 100, 50, and 200 pM, respectively (Voncken et al. 2002 Tjaden et al. 2004 Leroch et al. 2005 Leroch 2006) ...

A much slower transport process which catalyzes the net uptake of ATP has been demonstrated in liver [42,43] and heart mitochondria [44,45], and shown to be physiologically important in neonatal liver mitochondria [46,47]. The transporter s activity may be affected by hormones since it has been shown that glucagon treatment increases the total nucleotide content of subsequently isolated liver mitochondria [48]. Although initially thought to be due to rather nonspecific leakiness of mitochondrial membranes or unidirectional transport on the adenine nucleotide carrier, its lack of sensitivity to membrane potential, and its almost absolute dependence on the presence of Mg and phosphate suggest that the observed activity is due to a separate transporter [42]. Net nucleotide uptake in plant mitochondria is much more marked but has a similar dependence on Mg " and phosphate in the media [49]. 

The biosynthesis of the adenine nucleotide carrier has been studied most extensively in Neurospora crassa. The carrier isolated from Neurospora mitochondria is very similar to the carrier isolated from mammalian mitochondria [78]. Its molecular weight, subunit structure, amino acid composition, hydrophobicity and inhibitor specificity are remarkably similar to the mammalian heart and liver carriers. Specific antibodies to the Neurospora carrier have been raised in rabbits [79]. 

Although a few subunits of mitochondrial membrane proteins are coded by mitochondrial DNA and synthesized in the mitochondrial matrix, most membrane proteins including the adenine nucleotide carrier are coded by nuclear genes and synthesized on cytoplasmic ribosomes [80,81], Chloramphenicol, an inhibitor of mitochondrial protein synthesis, does not inhibit incorporation of radioactive leucine into the carrier in growing Neurospora crassa, but cycloheximide, an inhibitor of cytoplasmic protein synthesis, does inhibit leucine incorporation [78]. Also, a yeast nuclear respiratory mutant has been shown to cause a defect in adenine nucleotide transport [81], and the nuclear gene responsible for coding the carrier in yeast is currently being cloned for further studies [82]. 

A pool of adenine nucleotide carrier precursor protein has been identified in the... 

Deviation from expected kinetic behavior for the gated pore model has also been observed in the case of the two electrogenic transporters, the glutamate/aspartate and the adenine nucleotide carriers. 

Fig. 8.1. Two-dimensional schematic representation of the structure of the adenine nucleotide carrier. The line represents the amino acid chain of the protein and all numbers on or within the line represent the number of the amino acids in the linear sequence. The black dots are cysteine residues, about which there is significant sequence homology [186]. The helical regions are segments of hydrophobic amino acids thought to span the membrane [186]. The CAT arrow represents the site of photoaffinity labelling of an azido derivative of atractyloside [189]. The open circles are lysine residues which react with pyridoxal phosphate in intact mitochondria or submitochondrial particles [190,191].

At the present time, it is the opinion of the present reviewers that Wilson and collaborators have not provided sufficient evidence to conclude that the adenine nucleotide carrier is electroneutral and near equilibrium, nor have they conclusively shown that the first two sites of oxidative phosphorylation are in near equilibrium, especially in view of the likelihood that the P/O ratio of the first two sites is 1.5 rather than 2 [230,231]. Therefore, we conclude that their studies do not convincingly exclude a role for the adenine nucleotide translocator in the control of mitochondrial respiration. 

In general, mechanistic studies of the mitochondrial metabolite transporters carried out in the last five years have provided evidence supporting a gated-pore, sequential model for transport. Structural studies of the adenine nucleotide carrier are more advanced than studies of the other transporters, and these provide the most clear cut evidence. 

The mitochrondrial peripheral-type benzodiazepine receptor (PTBR) is a multimeric complex comprising three snbnnits, namely an 18 KDa isoqninoline crrrboxamine-binding protein (IBP), a 34 KDa voltage-dependent anion channel and a 30 KDa adenine nucleotide carrier (McEnery et al., 1992). 

Mans AM, De Joseph MR, Hawkins RA. Metabolic abnormalities and grade of encephalopathy in acute hepatic failure. J. Neurochem., 63, 1829-1838, 1994 McEnery MW, Snowman AM, Trifiletti RR, Snyder SH. Isolation of the mitochondrieil benzodiazepine receptor Association with the voltage-dependent anion channel tuid the adenine nucleotide carrier. Proc. Natl. Acad. Sci. USA, 89, 3170-3174, 1992 Mena EE, Cotman CW. Pathologic concentrations of ammonium ions block 1-gluttunate uptake. Exp. Neurol, 59, 259-263, 1985... 

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. 

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