Mitochondrial trifunctional protein

Matern D, Strauss AW, Hillman SL, Mayatepek E, Millington DS, Trefz FK (1999) Diagnosis of mitochondrial trifunctional protein deficiency in a blood spot from the newborn screening card by tandem mass spectrometry and DNA analysis. Pediatr Res 46 45-49... 

Hintz SR, Matern D, Strauss A, et al (2002) Early neonatal diagnosis of long-chain 3-hydroxy-acyl coenzyme a dehydrogenase and mitochondrial trifunctional protein deficiencies. Mol Genet Metab 75 120-127... 

K, Johnson, A.W., Bartlett, K. (2000) The mitochondrial trifunctional protein centre of a /3-oxidation metabolon Biochem. 

Ijlst L, Ruiter JP, Hoovers JM, Jakobs ME, Wanders RJ. Common missense mutation G1528C in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Characterization and expression of the mutant protein, mutation analysis on genomic DNA and chromosomal localization of the mitochondrial trifunctional protein alpha subunit gene. J Clin Invest 1996 98 1028-33. 

Yang Z, Yamada 1, Zhao Y, et al. Prospective screening for pediatric mitochondrial trifunctional protein defects in pregnancies complicated by liver disease. JAMA 2002 288 2163-66. 

Kamijo, T., Wanders, J.A., Saudubray, J.-M., Aoyama, T., Komiyama, A. Hashimoto, T. (1994) J. Clin. Invest. 93, 1740-1747. Mitochondrial trifunctional protein deficiency. Catalytic heterogeneity of the mutant enzyme in two patients. 

Ulst, L, Wanders, RJ.A, Ushikubo, S., Kamijo, T. Hashimoto, T. (1994) Biochim. Biophys. Acta., 1215, 347-350. Molecular basis of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency identification of the major disease-causing mutation in the a-subunit of the mitochondrial trifunctional protein. 

Enzymes 7,9, and 13 form a trifunctional protein associated with the inner face of the inner mitochondrial membrane. Very-long-chain acyl-CoA dehydrogenase is also associated with other inner mitochondrial membranes while the other enzymes are in the matrix and may be loosely associated with the inner face of the inner membrane. A medium-chain 2-enoyl-CoA hydratase may also be present in the mitochondrial matrix. 

The last three steps of this four-step sequence are catalyzed by either of two sets of enzymes, with the enzymes employed depending on the length of the fatty acyl chain. For fatty acyl chains of 12 or more carbons, the reactions are catalyzed by a multienzyme complex associated with the inner mitochondrial membrane, the trifunctional protein (TFP). TFP is a heterooctamer of 4/34 subunits. Each a subunit contains two activities, the enoyl-CoA hydratase and the /3-hydroxyacyl-CoA dehydrogenase the /3 subunits contain the thiolase activity. This tight association of three enzymes may allow efficient substrate channeling from one active site to the... 

The first three reactions are catalyzed by a trifunctional protein which contains carbamoyl-phosphate synthetase II, aspartate carbamoyltransferase and dihydro-orotase. This set of reactions begins with the synthesis of carbamoyl phosphate followed by its condensation with aspartic acid. The third step involves the closure of the ring through the removal of water by the action of dihydro-orotase to yield dihydro-orotate. The fourth enzyme, dihydro-orotate oxidase, oxidizes dihydro-orotate to orotate and is a mitochondrial flavoprotein enzyme located on the outer surface of the inner membrane and utilizes NAD" " as the electron acceptor. The synthesis of UMP from orotate is catalyzed by a bifunctional protein which comprises orotate PRTase and orotidine 5 -phosphate (OMP) decarboxylase. The former phosphoribosylates orotate to give OMP the latter decarboxylates OMP to UMP, the immediate precursor for the other pyrimidine nucleotides. It is interesting to note that whereas five molecules of ATP (including the ATP used in the synthesis of PRPP) are used in the de novo synthesis of IMP, no net ATP is used in the de novo synthesis of UMP. In de novo pyrimidine synthesis, two ATP molecules are used to synthesize carbamoyl phosphate and one ATP is needed to synthesize the PRPP used by orotate PRTase but 3 ATPs... 

Figure 4. Alignment of the amino acid sequence between His and Glu of the coli multifunctional protein (MP) with those of homologous regions of pig mitochondrial long-chain-specific bifunctional enzyme (LT), plant glyoxysomal tetrafunctional protein (PT), rat peroxisomal trifunctional enzyme (TE), and pig liver L-3-hydroxyacyl-CoA dehydrogenase (LD). The conserved histidine and glutamate residues are indicated by asterisks. The large subunit of human mitochondrial trifunctional P-oxidation complex has the same amino acid sequence as that of LT in this region. Qlu of MP corresponds to Glu of the large subunits of these mammalian p-oxidation complexes and to Glu of their precursors.

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