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Showing 51 - 60 of 48701 pathways
SMPDB ID Pathway Chemical Compounds Proteins


Pw000051 View Pathway

Valine, Leucine, and Isoleucine Degradation

Valine, isoleuciine, and leucine are essential amino acids and are identified as the branched-chain amino acids (BCAAs). The catabolism of all three amino acids starts in muscle and yields NADH and FADH2 which can be utilized for ATP generation. The catabolism of all three of these amino acids uses the same enzymes in the first two steps. The first step in each case is a transamination using a single BCAA aminotransferase, with α-ketoglutarate as the amine acceptor. As a result, three different α-keto acids are produced and are oxidized using a common branched-chain α-keto acid dehydrogenase (BCKD), yielding the three different CoA derivatives. Isovaleryl-CoA is produced from leucine by these two reactions, alpha-methylbutyryl-CoA from isoleucine, and isobutyryl-CoA from valine. These acyl-CoA’s undergo dehydrogenation, catalyzed by three different but related enzymes, and the breakdown pathways then diverge. Leucine is ultimately converted into acetyl-CoA and acetoacetate; isoleucine into acetyl-CoA and succinyl-CoA; and valine into propionyl-CoA (and subsequently succinyl-CoA). Under fasting conditions, substantial amounts of all three amino acids are generated by protein breakdown. In muscle, the final products of leucine, isoleucine, and valine catabolism can be fully oxidized via the citric acid cycle; in the liver, they can be directed toward the synthesis of ketone bodies (acetoacetate and acetyl-CoA) and glucose (succinyl-CoA). Because isoleucine catabolism terminates with the production of acetyl-CoA and propionyl-CoA, it is both glucogenic and ketogenic. Because leucine gives rise to acetyl-CoA and acetoacetyl-CoA, it is classified as strictly ketogenic.


Pw122411 View Pathway

2-Amino-3-Carboxymuconate Semialdehyde Degradation

This pathway is part of a major route of the degradation of L-tryptophan. It begins with 2-amino-3-carboxymuconate-6-semialdehyde which is generated from L-tryptophan degradation. The 2-amino-3-carboxymuconate-6-semialdehyde first is acted upon by a decarboxylase, forming 2-aminomuconic acid semialdehyde, which is then dehydrogenated by 2-aminomuconic semialdehyde dehydrogenase to form 2-aminomuconic acid. An unknown protein forms a 2-aminomuconate deaminase which forms (3E)-2-oxohex-3-enedioate, and a second unknown protein forms a 2-aminomuconate reductase, which forms oxoadipic acid from (3E)-2-oxohex-3-enedioate. Finally, within the mitochondria, oxoadipic acid is dehydrogenated and a coenzyme A is attached by the organelle’s oxoglutarate dehydrogenase complex, forming glutaryl-CoA. Glutaryl-CoA can then be further degraded.


Pw000032 View Pathway

Pantothenate and CoA Biosynthesis

Pantothenate, also called vitamin B5, is a nutrient that everyone requires in their diet. The nutrient gets its name from the greek word “pantothen” which means “from everywhere.” The reason it is called this is because pantothenic acid is found in almost every food. It is a precursor of coenzyme A, which is an essential part of many reactions in the body, specifically important in the production of compounds like cholesterol and different fatty acids. Most of pantothenic acid is found in food as phosphopentetheine or coenzyme A. Pantothenic acid, pantetheine 4’-phosphate and pantetheine are all found in red blood cells. The 6 step process in which coenzyme A is created begins with the creation of pantothenic acid from pantetheine, which is catalyzed by the enzyme pantetheinase. Pantothenic acid then works with pantothenate kinase 1 to produce D-4’-phosphopantothenate. This compound quickly becomes 4’phosphopantothenoylcysteine through the enzyme phosphopantothenate-cysteine ligase. 4’phosphopantothenoylcysteine then uses phosphopantothenoylcysteine decarboxylase to create pantetheine 4’-phosphate. This compound then undergoes two reactions, both resulting in the production of dephospho-CoA; the first reaction uses ectonucleotide pyrophosphatase/phosphodiesterase family member 1, the second uses bifunctional coenzyme A synthase. In the final step of coenzyme A synthesization, bifunctional coenzyme A synthase catalyzes dephospho-CoA into coenzyme A.


Pw000049 View Pathway

Lactose Synthesis

Lactose synthesis occurs only in the mammary glands, producing lactose (4-O-B-D-galactosylpyranosyl-a-D-glucopyranoside), the major sugar in milk. Lactose is created by joining two monosaccarides with a B1,4 glycosidic bond. Glucose is first converted to UDP-galactose via the enzyme galactose-1-phosphate uridylyltransferase. UDP-galactose is then transported into the Golgi by the UDP galactose translocator, an antiporter which uses facilitated transport to move UDP galactose into the Golgi and exports UMP. Once inside the Golgi, the UDP galactose and glucose (which moves into the golgi via the GLUT-1 transporter) become substrates for the lactose synthase enzyme complex, comprised of the enzymatic subunit, galactosyltransferase with its regulatory subunit, Alpha-lactalbumin. Lactose synthase creates lactose through bonding galactose from UDP to glucose through a glycosidic bond. Although GT is found in many tissues in the body, Alpha-lactalbumin is only found on the inner surface of the Golgi in the mammary glands, limiting lactose production to the mammaries.


Pw000044 View Pathway

Arachidonic Acid Metabolism

This pathway describes the production and subsequent metabolism of arachidonic acid, an omega-6 fatty acid. In resting cells arachidonic acid is present in the phospholipids (especially phosphatidylethanolamine and phosphatidylcholine) of membranes of the body’s cells, and is particularly abundant in the brain. Typically a receptor-dependent event, requiring a transducing G protein, initiates phospholipid hydrolysis and releases the fatty acid into the intracellular medium. Three enzymes mediate this deacylation reaction including phospholipase A2 (PLA2), phospholipase C (PLC), and phospholipase D (PLD). Once released, free arachidonate has three possible fates: 1) reincorporation into phospholipids, 2) diffusion outside the cell, and 3) metabolism. Arachidonate metabolism is carried out by three distinct enzyme classes: cyclooxygenases, lipoxygenases, and cytochrome P450’s. Specifically, the enzymes cyclooxygenase and peroxidase lead to the synthesis of prostaglandin H2, which in turn is used to produce the prostaglandins, prostacyclin, and thromboxanes. The enzyme 5-lipoxygenase leads to 5-HPETE, which in turn is used to produce the leukotrienes, hydroxyeicosatetraenoic acids (HETEs) and lipoxins. Some arachidonic acid is converted into midchain HETEs, omega-chain HETEs, dihydroxyeicosatrienoic acids (DHETs), and epoxyeicosatrienoic acids (EETs) by cytochrome P450 epoxygenase hydroxylase activity. Several products of these pathways act within neurons to modulate the activities of ion channels, protein kinases, ion pumps, and neurotransmitter uptake systems, affecting processes such as cellular proliferation, inflammation, and hemostasis. The newly formed eicosanoids may also exit the cell of origin and bind to G-protein-coupled receptors present on nearby neurons or glial cells.


Pw000025 View Pathway

Fructose and Mannose Degradation

Fructose and mannose are monosaccharides that can be found in many foods. Fructose can join with glucose to form sucrose. Mannose can be converted to glucose. Both may be used as food sweeteners. Fructose is well absorbed, especially in the presence of glucose. Fructose causes less of an insulin response compared to glucose and thus may be a preferred sugar for diabetics. In contrast to fructose, humans do not metabolize mannose well with the majority of it being excreted unchanged. Mannose in the urine can be beneficial in treating urinary tract infections caused be E. coli. However, mannose can be detrimental to humans by causing diabetic complications.


Pw000018 View Pathway

Cysteine Metabolism

The semi-essential amino aid cysteine is tightly regulated in the body to ensure proper levels for metabolism but maintaining levels below toxic thresholds. Cysteine can be obtained from diet or synthesized from O-acetyl-L-serine. Cystine is the dimeric form of cysteine. Cysteine is a precursor for protein synthesis and an antioxidant. Impaired cysteine metabolism has been linked with neurodegenerative disorders.


Pw000006 View Pathway

Alpha Linolenic Acid and Linoleic Acid Metabolism

Linoleic acid (LNA) is a polyunsaturated fatty acid (PUFA) precursor to the longer n−6 fatty acids commonly known as omega-6 fatty acids. Omega-6 fatty acids are characterized by a carbon-carbon double bond at the sixth carbon from the methyl group. Similarly, the PUFA alpha-linoleic acid (ALA) is the precursor to n-3 fatty acids known as omega-3 fatty acids which is characterized by a carbon-carbon double bond at the third carbon from the methyl group. Both LNA and ALA are essential dietary requirements for all mammals since they cannot be synthesized natively in the body. Both undergo a series of similar conversions to reach their final fatty acid form. LNA enters the cell and is catalyzed to gamma-linolenic acid (GLA) by acyl-CoA 6-desaturase (delta-6-desaturase/fatty acid desaturase 2). GLA is then converted to dihomo-gammalinolenic acid (DGLA) by elongation of very long chain fatty acids protein 5 (ELOVL5). DGLA is then converted to arachidonic acid (AA) by acyl-CoA (8-3)-desaturase (delta-5-desaturase/fatty acid desaturase 1). Arachidonic acid is then converted to a series of short lived metabolites called eicosanoids before finally reaching it's final fatty acid form.


Pw000013 View Pathway

Biotin Metabolism

Biotin is a vitamin that is an essential nutrient for humans. Biotin can be absorbed from consuming various foods such as: legumes, soybeans, tomatoes, romaine lettuce, eggs, cow's milk, oats and many more. Biotin acts as a cofactor for enzymes to catalyze carboxylation reactions involved in gluconeogenesis, amino acid catabolism and fatty acid metabolism. Biotin deficiency has been associated with many human diseases. These diseases may be caused by dysfunctional biotin metabolism due to enzyme deficiencies. Some research suggests biotin may play a role in transcription regulation or protein expression which may lead to biotin related diseases.


Pw000037 View Pathway

Spermidine and Spermine Biosynthesis

The Spermidine and Spermine Biosynthesis pathway highlights the creation of these cruicial polyamines. Spermidine and spermine are produced in many tissues, as they are involved in the regulation of genetic processes from DNA synthesis to cell migration, proliferation, differentiation and apoptosis. These positiviely charged amines interact with negatively charged phosphates in nucleic acids to exert their regulatory effects on cellular processes. Spermidine originates from the action of spermidine synthase, which converts the methionine derivative S-adenosylmethionine and the ornithine derivative putrescine into spermidine 5'-methylthioadenosine. Spermidine is subsequently processed into spermine by spermine synthase in the presence of the aminopropyl donor, S-adenosylmethioninamine.
Showing 51 - 60 of 48701 pathways