Browsing Pathways

Peptidoglycan is a net-like polymer which surrounds the cytoplasmic membrane of most bacteria and functions to maintain cell shape and prevent rupture due to the internal turgor.In E. coli K-12, the peptidoglycan consists of glycan strands of alternating subunits of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) which are cross-linked by short peptides. The pathway for constructing this net involves two cell compartments: cytoplasm and periplasmic space. The pathway starts with a beta-D-fructofuranose going through a mannose PTS permease, phosphorylating the compund and producing a beta-D-fructofuranose 6 phosphate. This compound can be obtained from the glycolysis and pyruvate dehydrogenase or from an isomerization reaction of Beta-D-glucose 6-phosphate through a glucose-6-phosphate isomerase.The compound Beta-D-fructofuranose 6 phosphate and L-Glutamine react with a glucosamine fructose-6-phosphate aminotransferase, thus producing a glucosamine 6-phosphate and a l-glutamic acid. The glucosamine 6-phosphate interacts with phosphoglucosamine mutase in a reversible reaction producing glucosamine-1P. Glucosamine-1p and acetyl coa undergo acetylation throuhg a bifunctional protein glmU releasing Coa and a hydrogen ion and producing a N-acetyl-glucosamine 1-phosphate. Glmu, being a bifunctional protein, follows catalyze the interaction of N-acetyl-glucosamine 1-phosphate, hydrogen ion and UTP into UDP-N-acetylglucosamine and pyrophosphate. UDP-N-acetylglucosamine then interacts with phosphoenolpyruvic acid and a UDP-N acetylglucosamine 1- carboxyvinyltransferase realeasing a phosphate and the compound UDP-N-acetyl-alpha-D-glucosamine-enolpyruvate. This compound undergoes a NADPH dependent reduction producing a UDP-N-acetyl-alpha-D-muramate through a UDP-N-acetylenolpyruvoylglucosamine reductase. UDP-N-acetyl-alpha-D-muramate and L-alanine react in an ATP-mediated ligation through a UDP-N-acetylmuramate-alanine ligase releasing an ADP, hydrogen ion, a phosphate and a UDP-N-acetylmuramoyl-L-alanine. This compound interacts with D-glutamic acid and ATP through UDP-N-acetylmuramoylalanine-D-glutamate ligase releasing ADP, A phosphate and UDP-N-acetylmuramoyl-L-alanyl-D-glutamate. The latter compound then interacts with meso-diaminopimelate in an ATP mediated ligation through a UDP-N-acetylmuramoylalanine-D-glutamate-2,6-diaminopimelate ligase resulting in ADP, phosphate, hydrogen ion and UDP-N-Acetylmuramoyl-L-alanyl-D-gamma-glutamyl-meso-2,6-diaminopimelate. This compound in turn with D-alanyl-D-alanine react in an ATP-mediated ligation through UDP-N-Acetylmuramoyl-tripeptide-D-alanyl-D-alanine ligase to produce UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-gama-D-glutamyl-meso-2,6-diaminopimeloyl-Dalanyl-D-alanine and hydrogen ion, ADP, phosphate. UDP-N-acetyl-alpha-D-muramoyl-L-alanyl-gama-D-glutamyl-meso-2,6-diaminopimeloyl-Dalanyl-D-alanine interacts with di-trans,octa-cis-undecaprenyl phosphate through a phospho-N-acetylmuramoyl-pentapeptide-transferase, resulting in UMP and N-Acetylmuramoyl-L-alanyl-D-glutamyl-meso-2,6-diaminopimelyl-D-alanyl-D-alanine-diphosphoundecaprenol which in turn reacts with a UDP-N-acetylglucosamine through a N-acetylglucosaminyl transferase to produce a hydrogen, UDP and Undecaprenyl-diphospho-N-acetylmuramoyl-(N-acetylglucosamine)-L-alanyl-D-glutaminyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine. This compound ends the cytoplasmic part of the pathway. Undecaprenyl-diphospho-N-acetylmuramoyl-(N-acetylglucosamine)-L-alanyl-D-glutaminyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine is transported through a lipi II flippase. Once in the periplasmic space, the compound reacts with a penicillin binding protein 1A prodducing a peptidoglycan dimer, a hydrogen ion, and UDP. The peptidoglycan dimer then reacts with a penicillin binding protein 1B producing a peptidoglycan with D,D, cross-links and a D-alanine.

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.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

In gram-negative bacteria, cytoplasmic and periplasmic isozymes of superoxide dismutase (SOD) is their defense system against superoxide anion (O2-). In E.coli, there are several SOD isozymes which are manganese-cofactored (MnSOD), iron-cofactored (FeSOD) and copper, zinc-cofactored (CuZnSOD) in perplasm, and they can be generated by autooxidation of dihydromenaquinone in the cytoplasmic membrane. In E.coli, MnSOD and FeSOD have similar structure and kinetic, but CuZnSOD is monomeric. FeSOD is the only SOD in E.coli under anaerobic conditions. MnSOD is induced by environmental stress condition as well as aerobic growth. CuZnSOD is induced in stationary phase. SOD will catalyze the superoxide anion to form oxygen and H2O2. With increasing concentration of H2O2, catalase such as cryptic adenine deaminase is induced in E.coli to degrade H2O2 into water and oxygen.

The degradation of cysteine starts with L-cysteine reacting with l-cysteine desulfhydrase resulting in the release of a hydrogen sulfide, a hydrogen ion and a a 2-aminoprop-2-enoate. The latter compound in turn reacts spontaneously to form a 2-iminopropanoate. This compound in turn reacts spontaneously with water and a hydrogen ion resulting in the release of ammonium and pyruvate.

The degradation of deoxycytidine starts with deoxycytidine being introduced into the cytosol through either a nupG or nupC symporter. Once inside, it can can be degrade through water,a hydrogen ion and a deoxycytidien deaminsa resultin in the release of a ammonium and a a deoxyuridine. The deoxyuridine is then degraded through a uracil phosphorylase resulting in the release of a deoxyribose 1-phosphate and a uracil. The degradation of thymidine starts with thymidine being introduced into the cytosol through either a nupG or nupC symporter. Thymidine is then degrades through a phosphorylase resulting in the release of a thymine and a deoxyribose 1-phosphate.

The degradation of of adenosine nucleotides starts with AMP reacting with water through a nucleoside monophosphate phosphatase results in the release of phosphate and a adenosine. Adenosine reacts with water and hydrogen ion through an adenosine deaminase resulting in the release of ammonium and a inosine. Inosine reacts with phosphate through a inosine phosphorylase resulting in the release of an alpha-D-ribose-1-phosphate and an hypoxanthine. Hypoxanthine reacts with a water molecule and a NAD molecule through an hypoxanthine hydroxylase resulting in the release of an hydrogen ion, an NADH and a xanthine. Xanthine in turn is degraded by reacting with a water molecule and a NAD through xanthine NAD oxidoreductase resulting in the release of NADH, a hydrogen ion and urate.

The pathway begins with the introduction of deoxycytidine into the cytosol, either through a nupG symporter or a nupC symporter. Once inside it is deaminated when reacting with a water molecule, a hydrogen ion and a deoxycytidine deaminase resulting in the release of an ammonium and a deoxyuridine. Deoxyuridine can also be imported through a nupG symporter or a nupC symporter. Deoxyuridine can react with an ATP through a deoxyuridine kinase resulting in the release of a ADP , a hydrogen ion and a dUMP. Deoxyuridine can also react with a phosphate through a uracil phosphorylase resulting in the release of a uracil and a deoxy-alpha-D-ribose 1-phosphate. This compound in turn reacts with a thymine through a thymidine phosphorylase resulting in the release of a phosphate and a thymidine. Thymidine in turn reacts with an ATP through a thymidine kinase resulting in a release of an ADP, a hydrogen ion and a dTMP

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.