Different types of substrate carrier proteins involved in energy transfer are found in the inner mitochondrial membrane [1,2,3,4,5]. These are:

• The ADP,ATP carrier protein (AAC) (ADP/ATP translocase) which exports ATP into the cytosol and imports ADP into the mitochondrial matrix. The sequence of AAC has been obtained from various mammalian, plant and fungal species.
• The 2-oxoglutarate/malate carrier protein (OGCP), which exports 2-oxoglutarate into the cytosol and imports malate or other dicarboxylic acids into the mitochondrial matrix. This protein plays an important role in several metabolic processes such as the malate/aspartate and the oxoglutarate/isocitrate shuttles.
• The phosphate carrier protein, which transports phosphate groups from the cytosol into the mitochondrial matrix.
• The brown fat uncoupling protein (UCP) which dissipates oxidative energy into heat by transporting protons from the cytosol into the mitochondrial matrix.
• The tricarboxylate transport protein (or citrate transport protein) which is involved in citrate-H+/malate exchange. It is important for the bioenergetics of hepatic cells as it provides a carbon source for fatty acid and sterol biosyntheses, and NAD for the glycolytic pathway.
• The Grave's disease carrier protein (GDC), a protein of unknown function recognized by IgG in patients with active Grave's disease.
• Yeast mitochondrial proteins MRS3 and MRS4. The exact function of these proteins is not known. They suppress a mitochondrial splice defect in the first intron of the COB gene and may act as carriers, exerting their suppressor activity by modulating solute concentrations in the mitochondrion.
• Yeast mitochondrial FAD carrier protein (gene FLX1).
• Yeast protein ACR1 [6], which seems essential for acetyl-CoA synthase activity.
• Yeast protein PET8.
• Yeast protein PMT.
• Yeast protein RIM2.
• Yeast protein YHM1/SHM1.
• Yeast protein YMC1.
• Yeast protein YMC2.
• Yeast hypothetical proteins YBR291c, YEL006w, YER053c, YFR045w, YHR002w, and YIL006w.
• Caenorhabditis elegans hypothetical protein K11H3.3.

Two other proteins have been found to belong to this family, yet are not localized in the mitochondrial inner membrane:

• Maize amyloplast Brittle-1 protein. This protein, found in the endosperm of kernels, could play a role in amyloplast membrane transport.
• Candida boidinii peroxisomal membrane protein PMP47 [7]. PMP47 is an integral membrane protein of the peroxisome and it may play a role as a transporter.

These proteins all seem to be evolutionary related. Structurally, they consist of three tandem repeats of a domain of approximately one hundred residues. Each of these domains contains two transmembrane regions.

The profile we developed covers the entire solute carrier (Solcar) repeat.