Browsing Pathways

Trehalose is a disaccharide made of two glucose molecules that can be used as a store of energy, as well as water retention and protection from freezing at low temperatures. In this pathway, glucose-6-phosphate from the galactose metabolism pathway combines with uridine diphosphate glucose to form alpha,alpha-trehalose 6-phosphate, as well as uridine 5’-diphosphate and a hydrogen ion as byroducts in a reaction catalyzed by alpha,alpha-trehalose-phosphate synthase [UDP-forming]. Following this, alpha,alpha-trehalose 6-phosphate is converted to alpha,alpha-trehalose following the hydrolytic cleavage of its phosphate group by trehalose-phosphate phosphatase. Alpha,alpha-trehalose can then function as energy stores until it is broken down as a part of the trehalose degradation pathway when needed.

Lipopolysaccharide (LPS) is a major component of outer membrane which is consisted of lipid A-core (oligosaccharide) on both inner and outer region and O-antigen (known as distal repeating unit with four sugars: N-acetylglucosamine, glucose, rhamnose and galactose). O-antigen is part of three domains of LPS, which is attached to lipid A-core; however, O-antigen and lipid A-core are synthesized separately. In this pathway, synthesis of three of O-antigen sugars is demonstrated. UDP-α-D-galactose is converted to UDP-D-Galacto-1,4-furanose by facilitation of UDP-galactopyranose mutase. dTTP glucose-1-phosphate is derivatized to dTDP-rhamnose. Fructose-6-phosphate gains an amino group, incorporates an acetate moiety and then acquires a nucleoside diphosphate resulting in UDP-N-acetyl-D-glucosamine.

This pathway demonstrates the degradation of extracellular putrescine in E.coli. Putrescine is imported by putrescine transporter (encoded by puuP gene). Putrescine is γ-glutamylated by activation of ATP which generates γ-glutamyl-putrescine, phosphate, and ADP. γ-glutamyl-putrescine is oxidized by gamma-glutamylputrescine oxidoreductase to form γ-glutamyl-γ-butyraldehyde, also produce ammonium and water. Gamma-glutamyl-gamma-aminobutyraldehyde dehydrogenase dehydrogenates γ-glutamyl-γ-butyraldehyde to γ-glutamyl-γ-aminobutyrate, which is then dehydrogenated into γ-Aminobutyric acid and L-Glutamic acid by γ-glutamyl-γ-aminobutyrate hydrolase.

Most bacteria, including Escherichia coli, are composed of murein which protects and stabilizes the cell wall. Over half of the murein is broken down by Escherichia coli and recycled for the next generation. The main muropeptide is GlcNAc-anhydro-N-acetylmuramic acid (anhMurNAc)-l-Ala-γ-d-Glu-meso-Dap-d-Ala which enters the cytoplasm by AmpG protein. The peptide is then released from the muropeptide. 1,6-Anhydro-N-acetylmuramic acid (anhMurNAc) is recycled by its conversion to N-acetylglucosamine-phosphate (GlcNAc-P). The sugar is phosphorylated by anhydro-N-acetylmuramic acid kinase (AnmK) to produce MurNAc-P. Etherase cleaves MurNAc-P to produce N-acetyl-D-glucosamine 6-phosphate. The product can undergo further degradation or be recycled into peptidoglycan monomers. The pathway's final product is a peptidoglycan biosynthesis precursor, UDP-N-acetyl-α-D-muramate. The enzyme muropeptide ligase (mpl), attaches the recovered Ala-Glu-DAP tripeptide to the precursor UDP-N-acetyl-α-D-muramate to return to the peptide to the peptidoglycan biosynthetic pathway to synthesize the cell wall.

The degradation of propanoyl-CoA starts with propanoyl-CoA undergoing a decarboxylase reaction by reacting with hydrogen carbonate and ATP resulting in the release of a phosphate, an ADP, a hydrogen ion and an S-methylmalonyl-CoA. This compound in turn reacts through an epimerase reaction resulting in the release of a R-methylmalonyl-CoA. This compound in turn can undergo a reversible reaction through a methylmalonyl-CoA mutase resulting in the release of a succinyl-CoA. This compound can be converted back to R-methylmalonyl-CoA through a methylmalonyl-CoA mutase. Methylmalonyl-CoA can then be converted into propanoyl-CoA through a methylmalonyl CoA decarboxylase . This compound in turn reacts with a succinate through a propionyl-CoA succinate CoA transferase resulting in the release of a propanoate and a succinyl-CoA.

Thiosulfate sulfurtransferase (also known as rhodanese) can facilitate the transfer of a sulfur atom from sulfur donors to nucleophilic sulfur acceptors, and it has been found in many major phyla (prokaryotic and eukaryotic). The role of thiosulfate sulfurtransferase might be the detoxification of cyanide in both bacteria and mammals, or it might also involve in formation of prosthetic groups in iron-sulfur proteins. In this pathway, thiosulfate and hydrogen cyanide have been catalyzed by thiosulfate sulfurtransferase to form thiocyanate and sulfite. Sulfite is used in later sulfur metabolism.

Sedoheptulose bisphospate bypass pathway demonstrates a series of reaction that form D-Erythrose 4-phosphate for pentose phosphate pathway and glycerone phosphate for glycolysis and pyruvate dehydrogenase pathway. D-Sedoheptulose 7-phosphate is obtained from pentose phosphate pathway, which later converted to sedoheptulose 1,7-bisphosphate via 6-phosphofructokinase-1. Fructose-bisphosphate aldolase class 2 catalyzes sedoheptulose 1,7-bisphosphate to form D-Erythrose 4-phosphate and pyruvate dehydrogenase.

2,3-Dihydroxybenzoate is created from chorismate through isochorismate and 2,3-dihydroxy-2,3-dihydrobenzoate. The biosynthesis of 2,3-dihydroxybenzoate starts from chorismate being converted into isochorismate through isochorismate synthase entC. The N-terminal isochorismate lyase domain of EntB adds hydrogen to the pyruvate group of isochorismate to create 2,3-dihydro-2,3-dihydroxybenzoate. this latter compound to 2,3-dihydroxybenzoate is then converted by the catalyzation of EntA dehydrogenase. This compound then interacts with L-serine and ATP through the enterobactin synthase protein complex resulting in the production of enterobactin. Enterobactin is exported into the periplasmic space through the enterobactin exporter entS. Enterobactin is then exported into the environment through the outer membrane protein TolC. In the environment, enterobactin reacts with iron to produce ferric enterobactin. It is then imported into the periplasmic space through a ferric enterobactin outer membrane transport complex. Ferric enterobactin continues it's journey and enters the cytoplasm via a ferric enterobactin ABC transporter. Once inside the cytoplasm, ferric enterobactin spontaneously releases the iron ion from the enterobactin. Alternatively, it can react with water through an enterochelin esterase resulting in the release of 2,3-dihydroxybenzoylserine, Fe3+, and hydrogen ions.

Asparagine is an amino acid used in protein synthesis, specifically the biosynthesis of glycoproteins. In E.coli, L-asparagine can be synthesized from L-aspartic acid by either utilizing asparagine synthetase B with L-glutamine or ammonia. Both reactions are driven by ATP however the reaction with ammonia utilizes both asparagine synthetase B and aspartate-ammonia ligase.

Spermidine metabolism starts with S-adenosyl-L-methionine reacting with a hydrogen ion through a adenosylmethionine decarboxylase resulting in the release of a carbon dioxide and a S-adenosyl 3-(methylthio)propylamine. The later compound in turn reacts with putrescine resulting in the release of a hydrogen ion, a spermidine and a S-methyl-5'-thioadenosine. S-methyl-5'-thioadenosine in turn reacts with a water molecule through a 5-methylthioadenosine nucleosidase resulting in the release of a adenine and a S-methyl-5-thio-D-ribose which in in turn is released into the environment.