Browsing Pathways

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.

Benzoate, an environmental pollutant, is utilized by bacteria such as Aromatoleum aromaticum to yield energy and carbon. While the precise transport mechanisms remain under research, it is proposed that benzoate is transported across the cell membrane passively or actively via transport proteins such as permeases and porins. Benzoate is then converted to benzoyl-CoA by benzoate-CoA ligase. Benzoyl-CoA is then used for phenylalanine metabolism and processes e.g., biosynthesis of alkaloids

Phospholipids are membrane components in E. coli. The major phospholipids of E. coli are phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. All phospholipids contain sn-glycerol-3-phosphate esterified with fatty acids at the sn-1 and sn-2 positions. The reaction starts from a glycerone phosphate (dihydroxyacetone phosphate) produced in glycolysis. The glycerone phosphate is transformed into an sn-glycerol 3-phosphate (glycerol 3 phosphate) by NADPH-driven glycerol-3-phosphate dehydrogenase. sn-Glycerol 3-phosphate is transformed to a 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid). This can be achieved by an sn-glycerol-3-phosphate acyltransferase that interacts either with a long-chain acyl-CoA or with an acyl-[acp]. The 1-acyl-sn-glycerol 3-phosphate is transformed into a 1,2-diacyl-sn-glycerol 3-phosphate (phosphatidic acid) through a 1-acylglycerol-3-phosphate O-acyltransferase. This compound is then converted into a CPD-diacylglycerol through a CTP phosphatidate cytididyltransferase. CPD-diacylglycerol can be transformed either into an L-1-phosphatidylserine or an L-1-phosphatidylglycerol-phosphate through a phosphatidylserine synthase or a phosphatidylglycerophosphate synthase, respectively. The L-1-phosphatidylserine transforms into L-1-phosphatidylethanolamine through a phosphatidylserine decarboxylase. On the other hand, L-1-phosphatidylglycerol-phosphate gets transformed into an L-1-phosphatidyl-glycerol through a phosphatidylglycerophosphatase. These 2 products combine to produce a cardiolipin and an ethanolamine. The L-1 phosphatidyl-glycerol can also interact with cardiolipin synthase resulting in a glycerol and a cardiolipin.

Toluene degradation allows bacteria to use toluene, a common environmental pollutant, as both a carbon and energy source. Toluene enters the bacterial cell by passive diffusion due to its hydrophobic nature. Once within the cell, toluene undergoes a variety of enzymatic reactions. The first step is for the Gamma-Subunit of benzylsuccinate synthase to convert it into benzylsuccinate. This intermediate is then converted to Benzylsuccinyl-CoA by subunit of Benzylsuccinate CoA-transferases. Subsequently, Benzylsuccinyl-CoA undergoes a series of enzymatic reactions to form Benzoylsuccinyl-CoA, and finally benzoyl-CoA, which enters the benzoate degradation pathway, providing the bacteria with energy and carbon for growth and survival.

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.

Glycolysis is a metabolic pathway consisting of ten reactions that convert glucose to pyruvate, releasing energy to form ATP and NADH. It occurs in two phases: the chemical priming phase and the energy-yielding phase. In the priming phase, D-glucose, which can be imported or derived from galactose metabolism, is phosphorylated to glucose-6-phosphate by a hexokinase-like enzyme, using ATP. This is then converted to fructose-6-phosphate, which is further phosphorylated to fructose-1,6-bisphosphate by 6-phosphofructokinase, also using ATP. Aldolase then splits fructose-1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, which can interconvert via triosephosphate isomerase. In the energy-yielding phase, glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate by glyceraldehyde-3-phosphate dehydrogenase, producing NADH in the process. ATP is generated when 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate. Further steps involve the conversion of 3-phosphoglycerate to 2-phosphoglycerate by phosphoglycerate mutase, followed by conversion to phosphoenolpyruvate by enolase. Finally, pyruvate kinase converts phosphoenolpyruvate to pyruvate, producing ATP in the process. Pyruvate then participates in further metabolic pathways, including pyruvate metabolism, tyrosine metabolism, and the synthesis of pantothenate and CoA.

Fatty acid oxidation is also known as beta-oxidation. Fatty acids are an important energy source because they are anhydrous and can be reduced. Fatty acids are good sources of energy as they yield more energy than carbohydrates. The fatty acid oxidation pathway degrades fatty acids into acetyl-CoA under anaerobic and aerobic conditions. Enzymes of this pathway can process short and long chain fatty acids. The first step in the pathway is the conversion of acyl-CoA to enoyl-CoA. The pathway continues in a cycle, each turn removing two carbon atoms from the input acyl-CoA to produce acetyl-CoA. Each turn also produces NADH.

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.

Adenosine is first incorporated into the cytosol through either a nupG or a nupC transporter. Once in the cytosol, adenosine is degraded into adenine by reacting with a water and a adenosine nucleosidase, releasing a D-ribofuranose and a adenine. The adenine then reacts with a PRPP through a adenine phosphoribosyltransferase resulting in the release of a pyrophosphate and an AMP . The AMP in turn reacts with a water molecule through a AMP nucleosidase resulting in the release of a D-ribofuranose 5-phosphate and a adenine.