Disease relevance of ECs5231

• The quaternary structures of these two allosteric transcarbamoylases are quite divergent: the E. coli ATCase has pseudo-32 point-group symmetry, with six catalytic and six regulatory chains; the catabolic OTCase has 23 point-group symmetry and only catalytic chains [1].
• The crystal structure of the Glu-105-->Gly mutant of catabolic ornithine transcarbamoylase (OTCase; carbamoyl phosphate + L-ornithine = orthophosphate + L-citrulline, EC 2.1.3.3) from Pseudomonas aeruginosa has been determined at 3.0-A resolution [1].
• Metabolic enzymes from psychrophilic bacteria: challenge of adaptation to low temperatures in ornithine carbamoyltransferase from Moritella abyssi [2].
• Phaseolotoxin [(N delta-phosphosulfamyl)ornithylalanylhomoarginine], a phytotoxic tripeptide produced by Pseudomonas syringae pv. phaseolicola that inhibits ornithine carbamoyltransferase, is transported into Escherichia coli and Salmonella typhimurium via the oligopeptide transport system (Opp) [3].
• We have inserted a gene coding for ornithine transcarbamylase (OTCase) from Escherichia coli K-12 into the late gene region of simian virus 40 (SV40) DNA and propagated the hybrid molecules as free episomes or by co-infection with an SV40 tsA helper virus [4].

High impact information on ECs5231

• In contrast, the other domain, mainly implicated in the binding of the second substrate (ornithine for OTCase and aspartate for ATCase) is poorly conserved [1].
• The catabolic OTCase lost most of its homotropic cooperativity and gained anabolic activity when an amino acid residue near the CP binding site, Glu-106, was replaced by alanine or glycine [5].
• Thus, in catabolic OTCase, sequence features in addition to Glu-106 are important for sigmoidal CP saturation, and such a sequence was identified in the C-terminal part [5].
• In the anabolic OTCase of Escherichia coli the glutamine residue corresponding to Glu-106 was exchanged for glutamate; however, in this case no CP cooperativity was acquired [5].
• By an in vivo gene fusion technique the 9 C-terminal amino acids of catabolic OTCase were replaced by the homologous 8 amino acids from anabolic OTCase of E. coli; the hybrid enzyme had a markedly reduced homotropic cooperativity [5].

Chemical compound and disease context of ECs5231

• Escherichia coli ornithine transcarbamylase (OTCase) catalyzes the production of L-citrulline and phosphate from carbamyl phosphate and L-ornithine in L-arginine biosynthesis [6].
• In Pseudomonas aeruginosa PAO the anabolic ornithine carbamoyltransferase (OTCase, EC 2.1.3.3) is the product of the argF gene and the only arginine biosynthetic enzyme whose synthesis is repressible by arginine [7].
• On this basis, structural features of Escherichia coli ornithine transcarbamoylase (OTCase) were investigated by site-directed mutagenesis experiments based on the known tertiary structure of the catalytic (c) chain of E. coli aspartate transcarbamoylase (ATCase) [8].
• 13C isotope effects were measured in carbamyl phosphate, using OTCase obtained from E. coli in a one-column purification which yielded 30 mg of very pure enzyme from 51 of cell culture [9].

Biological context of ECs5231

• Allosteric regulation in Pseudomonas aeruginosa catabolic ornithine carbamoyltransferase revisited: association of concerted homotropic cooperative interactions and local heterotropic effects [10].
• The deduced amino acid sequence of the anabolic OTCase consists of 305 residues (Mr 33,924), and this was confirmed by the N-terminal amino acid sequence, the total amino acid composition, and the subunit Mr of the purified enzyme [7].
• Anabolic ornithine carbamoyltransferase of Pseudomonas aeruginosa: nucleotide sequence and transcriptional control of the argF structural gene [7].
• A fragment of DNA from a yeast Pachysolen tannophilus, bearing the ornithine carbamoyltransferase gene (OCTase, EC 2.1.3.3) has been cloned from a genomic library by functional complementation of the Escherichia coli OCT-negative mutant [11].
• The arcABC operon of Pseudomonas aeruginosa encodes arginine deiminase, catabolic ornithine carbamoyltransferase and carbamate kinase, respectively [12].

Associations of ECs5231 with chemical compounds

• Activation by AMP and inhibition by spermidine of this chimaeric OTCase do not affect carbamoylphosphate homotropic co-operativity [10].
• While inhibition of OTCase can lead to arginine auxotrophy, P. savastanoi pv. phaseolicola is able to synthesize toxin while growing on minimal medium [13].
• In UV difference and 31P-NMR spectra, carbamyl phosphate-induced effects associated with wild-type OTCase are observed in the R57G mutant only in the presence of guanidine [6].

Analytical, diagnostic and therapeutic context of ECs5231

• Multifrequency (2-230 MHz) phase-modulation fluorescence measurements and site-directed mutagenesis have been employed to assign fluorescence lifetimes, quantum yields, and emission maxima to the four tryptophans in the enzyme ornithine transcarbamoylase from Escherichia coli (OTCase) (Trp-125, -92, -233, and -243) [14].
• CONCLUSIONS: Our newly established ELISA for OCT using monoclonal antibodies is sensitive enough for clinical application [15].

References