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Showing 41 - 50 of 48701 pathways
SMPDB ID Pathway Chemical Compounds Proteins


Pw000149 View Pathway

Propanoate Metabolism

This pathway depicts the metabolism of propionic acid. Propionic acid in mammals typically arises from the production of the acid by gut or skin microflora. Propionic acid producing bacteria (Propionibacterium sp.) are particularly common in sweat glands of mammals. After entering a cell, the propionic acid (propanoate) then enters the mitochondria where it is converted into propanol adenylate (or propionyl adenylate or propionyl-AMP) via propionyl-CoA synthetase and acetyl-CoA synthetase. The propionyl adenylate then is converted into propionyl coenzyme A (propionyl-CoA) via the same pair of enzymes. Propionyl-CoA is a relatively common compound that can also arise from the metabolic breakdown of fatty acids containing odd numbers of carbon atoms. Propionyl-CoA is also known to arise from the breakdown of some amino acids. Since propanoate has three carbons, propionyl-CoA cannot directly enter the beta-oxidation cycle (which requires two carbons from acetyl-CoA). Therefore, in most vertebrates, propionyl-CoA is carboxylated into D-methylmalonyl-CoA via propionyl-CoA carboxylase. The resulting compound is isomerized into L-methylmalonyl-CoA via methylmalonyl-CoA epimerase. A vitamin B12-dependent enzyme, called methylmalonyl CoA mutase catalyzes the rearrangement of L-methylmalonyl-CoA to succinyl-CoA, which is an intermediate of the citric acid cycle. Also depicted in this pathway is another propionic acid homolog called hydroxypropanoic acid (hydroxypropionate). This compound is also produced by bacteria and imported into cells. Hydroxypropionate can be converted into 3-hydroxypropionyl-CoA. This compound can be either enzymatically converted to acryloyl-CoA and then to propionyl-CoA or it can spontaneously convert to malonyl-CoA. Malonyl-CoA can convert into acetyl-CoA (via acetyl-CoA carboxylase in the cytoplasm or malonyl carboxylase in the mitochondria) whereupon it may enter a variety of pathways. In a rare genetic metabolic disorder called propionic acidemia, propionate acts as a metabolic toxin in liver cells by accumulating in the liver mitochondria as propionyl-CoA and its derivative methylcitrate. Both propionyl-CoA and methylcitrate are known TCA inhibitors. Glial cells are particularly susceptible to propionyl-CoA accumulation. In fact, when propionate is infused into rat brains and take up by the glial cells, it leads to behavioural changes that resemble autism (PMID: 16950524).


Pw000017 View Pathway

Catecholamine Biosynthesis

The Catecholamine Biosynthesis pathway depicts the synthesis of catecholamine neurotransmitters. Catecholamines are chemical hormones released from the adrenal glands as a response to stress that activate the sympathetic nervous system. They are composed of a catechol group and are derived from amino acids. The commonly found catecholamines are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine. They are synthesized in catecholaminergic neurons by four enzymes, beginning with tyrosine hydroxylase (TH), which generates L-DOPA from tyrosine. The L-DOPA is then converted to dopamine via aromatic L-amino acid decarboxylase (AADC), which becomes norepinephrine via dopamine beta-hydroxylase (DBH); and finally is converted to epinephrine via phenylethanolamine N-methyltransferase (PNMT).


Pw000012 View Pathway

Betaine Metabolism

Betaine (or trimethylglycine) is similar to choline (trimethylaminoethanol) but differs in choline's terminal carboxylic acid group trimethylglycine is reduced to a hydroxyl group. Betaine is obtained from diet as betaine or compounds containing choline in foods such as whole grains, beets and spinach. Betaine can also be synthesized from choline in the liver and kidney. First, choline is oxidized to betaine aldehyde by mitochondrial choline oxidase (choline dehydrogenase). Then, betaine aldehyde dehydrogenase oxidizes betaine aldehyde to betaine in the mitochondria or cytoplasm. In the liver, betaine functions as a methyl donor similar to choline, folic acid, S-adenosyl methionine and vitamin B12. Methyl donors are important for liver function, cellular replication and detoxification reactions. Betaine is also involved in the production of carnitine to protect from kidney damage and functions as an osmoprotectant in the inner medulla.


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 41 - 50 of 48701 pathways