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.

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.

The metabolism of L-arginine starts with the acetylation of L-glutamic acid resulting in a N-acetylglutamic acid while releasing a coenzyme A and a hydrogen ion. N-acetylglutamic acid is then phosphorylated via an ATP driven acetylglutamate kinase which yields a N-acetyl-L-glutamyl 5-phosphate. This compound undergoes a NDPH dependent reduction resulting in N-acetyl-L-glutamate 5-semialdehyde, which then reacts with L-glutamic acid through a acetylornithine aminotransferase / N-succinyldiaminopimelate aminotransferase to produce an N-acetylornithine. Next N-acetylornithine is deacetylated through a acetylornithine deacetylase yielding an ornithine. L-glutamine is used to synthesize carbamoyl phosphate through the interaction of L-glutamine, water, ATP, and hydrogen carbonate. This reaction yields ADP, L-glutamic acid, phosphate, and hydrogen ion. Carbamoyl phosphate and ornithine are used to catalyze the production of citrulline through an ornithine carbamoyltransferase. Citrulline reacts with L-aspartic acid through an ATP dependent enzyme, argininosuccinate synthase to produce pyrophosphate, AMP and argininosuccinic acid. Argininosussinic acid is then lyase to produce L-arginine and fumaric acid. L-arginine can be metabolized into succinic acid by two different sets of reactions: 1. Arginine reacts with succinyl-CoA through a arginine N-succinyltransferase resulting in N2-succinyl-L-arginine while releasing CoA and Hydrogen Ion. N2-succinyl-L-arginine is then dihydrolase to produce a N2-succinyl-L-ornithine through a N-succinylarginine dihydrolase which in turn reacts with oxoglutaric acid through succinylornithine transaminase resulting in L-glutamic acid and N2-succinyl-L-glutamic acid 5-semialdehyde. Next N2-succinyl-L-glutamic acid 5-semialdehyde reacts with a NAD dependent dehydrogenase resulting in N2-succinylglutamate and releases NADH and hydrogen ion. Finally, N2-succinylglutamate reacts with water through a succinylglutamate desuccinylase resulting in L-glutamic acid and a succinic acid. The succinic acid is then incorporated in the TCA cycle 2. Argine reacts with carbon dioxide and a hydrogen ion through a biodegradative arginine decarboxylase, resulting in Agmatine. Agmatine is transformed into putrescine by reacting with water and an agmatinase, and releasing urea. Putrescine can be metabolized by reaction with either l-glutamic acid or oxoglutaric acid. If putrescine reacts with L-glutamic acid, it reacts through an ATP mediated gamma-glutamylputrescine producing a hydrogen ion, ADP, phosphate and gamma-glutamyl-L-putrescine. Gamma-glutamyl-L-putrescine is reduced via interactions with oxygen, water and a gamma-glutamylputrescine oxidoreductase resulting in ammonium, hydrogen peroxide and 4-gamma-glutamylamino butanal. Dehydrogenated through a NADP mediated reaction lead by gamma-glutamyl-gamma-aminobutaryaldehyde dehydrogenase, 4-gamma-glutamylamino butanal is converted into hydrogen ions, NADPH and 4-glutamylamino butanoate. In turn, the latter compound reacts with water through a gamma-glutamyl-gamma-aminobutyrate hydrolase resulting in L-glutamic acid and Gamma aminobutyric acid. On the other hand, if putrescine reacts with oxoglutaric acid through a putrescine aminotransferase, it results in L-glutamic acid, and a 4-aminobutyraldehyde, which continues and reacts with water through a NAD dependent gamma aminobutyraldehyde dehydrogenase resulting in hydrogen ion, NADH and gamma-aminobutyric acid. Gamma Aaminobutyric acid reacts with oxoglutaric acid through 4-aminobutyrate aminotransferase resulting in L-glutamic acid and succinic acid semialdehyde. Succinic acid semialdehyde then reacts with either NADP or NAD to produce succinic acid through succinate-semialdehyde dehydrogenase or aldehyde dehydrogenase-like protein yneI respectively. Succinic acid can then be integrated in the TCA cycle.

Vitamin B6 metabolism in bacteria involves the biosynthesis and utilization of various forms of Vitamin B6, primarily pyridoxal 5'-phosphate (PLP), the active form of the vitamin. Bacteria can synthesize Vitamin B6 through two main pathways: the de novo DXP-independent pathway (pyridoxal phosphate biosynthesis I) and the DXP-dependent pathway. In the de novo pathway, key enzymes like Pdx1 and Pdx2 convert intermediates into pyridoxine 5'-phosphate (PNP), which is then oxidized to PLP by the enzyme pyridoxine phosphate oxidase (PdxH). PLP acts as a cofactor for various enzymes involved in amino acid metabolism, including transaminases, decarboxylases, and racemases.Bacteria rely on PLP for critical cellular processes, including amino acid metabolism, stress response, and protection against oxidative damage.

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.

Streptomyces coelicolor is a soil-dwelling bacterium that is medically important due to its ability to produce several antibiotics, and nickel accumulation within this organism has been shown to prevent the production of the antibiotic undecylprodigiosin. The transcriptional repressor important in regulation of nickel uptake is the homodimeric Nur. Under nickel-sufficient conditions, Nur binds Ni²⁺ ions, undergoes a conformational change, and binds to DNA to repress transcription of nickel uptake genes. When intracellular Ni²⁺ is limited, Nur repression is lifted, allowing expression of nickel transporters to restore optimal levels. The nickel ion (Ni²⁺) effector pathway is essential for regulating nickel homeostasis in bacteria, ensuring the proper uptake of this important but potentially toxic trace metal. This pathway is regulated by Nur (Nickel uptake regulator), a Ni²⁺-responsive transcriptional repressor that controls the expression of genes involved in nickel transport and homeostasis. Key genes in the Nur regulog include: nikA – Encodes the periplasmic nickel-binding protein of the high-affinity NikABCDE ABC transporter system, which captures nickel ions and delivers them to the transporter. nikB, nikC, nikD, nikE – These genes encode the membrane-spanning and ATPase components of the NikABCDE transporter complex. Together, they form a high-affinity nickel uptake system that imports Ni²⁺ across the membrane into the cytoplasm.

The metabolism of L-arginine starts with the acetylation of L-glutamic acid resulting in a N-acetylglutamic acid while releasing a coenzyme A and a hydrogen ion. N-acetylglutamic acid is then phosphorylated via an ATP driven acetylglutamate kinase which yields a N-acetyl-L-glutamyl 5-phosphate. This compound undergoes a NDPH dependent reduction resulting in N-acetyl-L-glutamate 5-semialdehyde, which then reacts with L-glutamic acid through a acetylornithine aminotransferase / N-succinyldiaminopimelate aminotransferase to produce an N-acetylornithine. Next N-acetylornithine is deacetylated through a acetylornithine deacetylase yielding an ornithine. L-glutamine is used to synthesize carbamoyl phosphate through the interaction of L-glutamine, water, ATP, and hydrogen carbonate. This reaction yields ADP, L-glutamic acid, phosphate, and hydrogen ion. Carbamoyl phosphate and ornithine are used to catalyze the production of citrulline through an ornithine carbamoyltransferase. Citrulline reacts with L-aspartic acid through an ATP dependent enzyme, argininosuccinate synthase to produce pyrophosphate, AMP and argininosuccinic acid. Argininosussinic acid is then lyase to produce L-arginine and fumaric acid. L-arginine can be metabolized into succinic acid by two different sets of reactions: 1. Arginine reacts with succinyl-CoA through a arginine N-succinyltransferase resulting in N2-succinyl-L-arginine while releasing CoA and Hydrogen Ion. N2-succinyl-L-arginine is then dihydrolase to produce a N2-succinyl-L-ornithine through a N-succinylarginine dihydrolase which in turn reacts with oxoglutaric acid through succinylornithine transaminase resulting in L-glutamic acid and N2-succinyl-L-glutamic acid 5-semialdehyde. Next N2-succinyl-L-glutamic acid 5-semialdehyde reacts with a NAD dependent dehydrogenase resulting in N2-succinylglutamate and releases NADH and hydrogen ion. Finally, N2-succinylglutamate reacts with water through a succinylglutamate desuccinylase resulting in L-glutamic acid and a succinic acid. The succinic acid is then incorporated in the TCA cycle 2. Argine reacts with carbon dioxide and a hydrogen ion through a biodegradative arginine decarboxylase, resulting in Agmatine. Agmatine is transformed into putrescine by reacting with water and an agmatinase, and releasing urea. Putrescine can be metabolized by reaction with either l-glutamic acid or oxoglutaric acid. If putrescine reacts with L-glutamic acid, it reacts through an ATP mediated gamma-glutamylputrescine producing a hydrogen ion, ADP, phosphate and gamma-glutamyl-L-putrescine. Gamma-glutamyl-L-putrescine is reduced via interactions with oxygen, water and a gamma-glutamylputrescine oxidoreductase resulting in ammonium, hydrogen peroxide and 4-gamma-glutamylamino butanal. Dehydrogenated through a NADP mediated reaction lead by gamma-glutamyl-gamma-aminobutaryaldehyde dehydrogenase, 4-gamma-glutamylamino butanal is converted into hydrogen ions, NADPH and 4-glutamylamino butanoate. In turn, the latter compound reacts with water through a gamma-glutamyl-gamma-aminobutyrate hydrolase resulting in L-glutamic acid and Gamma aminobutyric acid. On the other hand, if putrescine reacts with oxoglutaric acid through a putrescine aminotransferase, it results in L-glutamic acid, and a 4-aminobutyraldehyde, which continues and reacts with water through a NAD dependent gamma aminobutyraldehyde dehydrogenase resulting in hydrogen ion, NADH and gamma-aminobutyric acid. Gamma Aaminobutyric acid reacts with oxoglutaric acid through 4-aminobutyrate aminotransferase resulting in L-glutamic acid and succinic acid semialdehyde. Succinic acid semialdehyde then reacts with either NADP or NAD to produce succinic acid through succinate-semialdehyde dehydrogenase or aldehyde dehydrogenase-like protein yneI respectively. Succinic acid can then be integrated in the TCA cycle.