Disease relevance of Otc

• Selection of a cDNA clone which contains the complete coding sequence for the mature form of ornithine transcarbamylase from rat liver: expression of the cloned protein in Escherichia coli. Molecular cloning of rat ornithine transcarbamylase [1].
• A cDNA clone corresponding to the mature form of ornithine transcarbamylase (OTCase) was selected from a rat liver cDNA library constructed in bacteriophage lambda gt10 [1].
• Promoter and 11-kilobase upstream enhancer elements responsible for hepatoma cell-specific expression of the rat ornithine transcarbamylase gene [2].
• Zinc supplementation reduces blood ammonia and increases liver ornithine transcarbamylase activity in experimental cirrhosis [3].
• 4. Sepsis increased the activities of liver carbamoylphosphate synthase (by 16.4%), ornithine transcarbamylase (by 29.8%), argininosuccinate synthase (by 28.1%) and arginase (by 33.8%) [4].

High impact information on Otc

• Import of rat ornithine transcarbamylase precursor into mitochondria: two-step processing of the leader peptide [5].
• Substitution of either an acidic (aspartate) or a "helix-breaking" (glycine) amino acid residue for arginine 23 of the leader inhibits formation of both iOTC and OTC, without affecting translocation [5].
• The mitochondrial matrix enzyme ornithine transcarbamylase (OTC) is synthesized on cytoplasmic polyribosomes as a precursor (pOTC) with an NH2-terminal extension of 32 amino acids [5].
• The same intermediate-sized OTC is produced in vivo in frog oocytes injected with in vitro-synthesized pOTC [5].
• In the first step, which is dependent upon an intact mitochondrial membrane potential, pOTC is translocated into mitochondria and cleaved by a matrix protease to a product designated iOTC, intermediate in size between pOTC and mature OTC [5].

Chemical compound and disease context of Otc

• OTC was studied in two groups of rats treated with carbon tetrachloride (CCl4): the first received zinc in the drinking water during the induction of cirrhosis; the second was the control group [6].

Biological context of Otc

• A cDNA clone for the precursor of rat mitochondrial ornithine transcarbamylase: comparison of rat and human leader sequences and conservation of catalytic sites [7].
• We have deduced the amino acid sequence of the N-terminal leader peptide of the mitochondrial enzyme ornithine transcarbamylase from a cDNA clone obtained from a rat liver cDNA library [8].
• An analysis of levels of RNA in fetal and neonatal liver shows that ornithine transcarbamylase mRNA levels increase from about 40% of adult levels at day 14 of gestation to a peak at day 20 of gestation, and, after a drop around the time of birth, rises to adult levels during the second week after birth [9].
• We have characterized further the biogenesis in vitro of ornithine transcarbamylase, a homotrimeric mitochondrial matrix enzyme synthesized in the cytoplasm as a larger precursor [10].
• OTC gene expression in the liver of BD rats was 40% lower than in BS rats (P < 0.05) [11].

Anatomical context of Otc

• Ornithine transcarbamylase, one of the enzymes of the urea cycle in ureotelic organisms, is synthesized in the cytoplasm of hepatocytes as a precursor larger than the mature form found in the mitochondrial matrix [9].
• The precursor of rat liver ornithine transcarbamylase (ornithine carbamoyltransferase; carbamoylphosphate:L-ornithine carbamoyltransferase, EC 2.1.3.3) (pre-ornithine transcarbamylase), which was synthesized in a reticulocyte lysate cell-free system, was converted to an apparently mature form of the enzyme by isolated rat liver mitochondria [12].
• The gene for ornithine transcarbamylase (OTC; EC 2.1.3.3), a urea cycle enzyme, is expressed almost exclusively in the liver and small intestine [2].
• Pulse-chase experiments showed that the ornithine transcarbamylase precursor and the thiolase traveled from the cytosol to the mitochondria with half-lives of less than 5 min, whereas the three fusion proteins traveled with half-lives of 10-15 min [13].
• The import behavior of the purified chimera, composed of the amino-terminal leader peptide of the rat ornithine transcarbamylase (OTC) and a double stranded DNA molecule (17 bp or 322 bp), was tested by incubating with coupled and 'energized' rat liver mitochondria in the presence of reticulocyte lysate [14].

Associations of Otc with chemical compounds

• We have investigated the putative carbamylphosphate- and ornithine-binding domains in ornithine transcarbamylase from rat liver using site-directed mutagenesis [15].
• Synthesis, intracellular transport, and processing of the precursors for mitochondrial ornithine transcarbamylase and carbamoyl-phosphate synthetase I in isolated hepatocytes [16].
• The synthesis and intracellular transport of the mitochondrial matrix enzymes ornithine transcarbamylase (carbamoylphosphate: L-ornithine carbamoyltransferase, EC 2.1.3.3.) and carbamoyl-phosphate synthetase (ammonia) I [carbon-dioxide:ammonia ligase (ADP-forming, carbamate-phosphorylating), EC 6.3.4.16] were studied in isolated rat hepatocytes [16].
• The results reported suggest the existence of interactions between carbamyl phosphate synthetase and ornithine transcarbamylase in the matrix [17].
• The finding that ornithine transcarbamylase can be limiting for citrulline synthesis shows that the activity of this enzyme is greatly restricted in mitochondria [17].

Other interactions of Otc

• OTCase clones were selected using a synthetic DNA probe of 15 bases corresponding to the 3' end of the OTCase mRNA [Horwich, A. L., Kraus, J.P., Williams, K., Kalousek, F., Königsberg, W. & Rosenberg, L.E. (1983) Proc. Natl Acad. Sci. USA, 80, 4258-4262] [1].
• Channeling of citrulline from its site of synthesis by ornithine transcarbamylase in the mitochondrial matrix to argininosuccinate synthetase in the cytoplasmic space was also shown [18].
• The concentration of digitonin required was higher than that for the intermembrane space enzyme, adenylate kinase (EC 2.7.4.3), but lower than that for endogenous ornithine transcarbamylase, which is localized in the matrix space [19].
• In contrast, the mRNA for heme oxygenase was elevated by hemin treatment, whereas the mRNA levels of beta-actin, albumin, and ornithine transcarbamylase, used as controls, were not affected [20].
• Arginase and ornithine transcarbamylase levels were analysed only in male rats and were found to be elevated in obese rats as compared to lean littermates [21].

Analytical, diagnostic and therapeutic context of Otc

• Site-directed mutagenesis of Arg60 and Cys271 in ornithine transcarbamylase from rat liver [15].
• The relative half-life of ornithine transcarbamylase from rat liver has been determined using the double isotope technique and affinity chromatography [22].
• Proof of expression of the rat enzyme in transformants was obtained by immunoprecipitation of all ornithine transcarbamylase activity from cell extracts with antibodies specific for the rat enzyme [23].
• For light microscopy, tissue slices of the digestive system were embedded in Epon and stained by using anti-bovine OTC rabbit IgG and the immunoenzyme technique [24].
• Electron microscopy showed that gold particles representing the antigenic sites for OTC were confined to the mitochondrial matrix of hepatocytes and small intestinal epithelial cells [24].

References