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Showing 31 - 40 of 48701 pathways
SMPDB ID Pathway Chemical Compounds Proteins


Pw122268 View Pathway

Kidney Function- Proximal Convoluted Tubule

The proximal convoluted tubule is part of the nephron between the Bowman's capsule and the loop of Henle. The proximal convoluted tubule functions to reabsorb sodium, water, and other ions. Sodium and bicarbonate (hydrogen carbonate) are transported by a co-transporter that is responsible for the majority of sodium reabsorption. The bicarbonate, along with hydrogen, are exchanged across the basal and apical membranes, respectively, to effectively regulate the pH of the filtrate. In addition, chloride ions are not normally reabsorbed in large amounts at the proximal tubule compared to other parts of the nephron. However, the reabsorption of chloride, as well as potassium, increases as the amount of water reabsorption increases due to solvent drag (also known as bulk transport). This occurrence explains solute movement secondary to water flow. All the cation and anion transport creates a gradient favourable for ion and water reabsorption, leading to an increase in blood pressure.


Pw000055 View Pathway

Pentose Phosphate Pathway

The pentose phosphate pathway—also referred to in the literature as the phosphogluconate pathway, the hexose monophosphate shunt, or the pentose phosphate shunt—is involved in the generation of NADPH as well as pentose sugars. Of the total cytoplasmic NADPH used in biosynthetic reactions, a significant proportion of it is generated through the pentose phosphate pathway. Ribose 5-phosphate is also another essential product generated by this pathway which is employed in nucleotide synthesis. The pentose phosphate pathway is also involved in the digestive process as the products of nucleic acid catabolism can be metabolized through the pathway (pentose sugars are usually yielded in the breakdown) while the carbon backbones of dietary carbohydrates can be converted into glycolytic/gluconeogenic intermediates. The pentose phosphate pathway is interconnected to the glycolysis pathway through the shared use of three intermediates: glucose 6-phosphate, glyceraldehyde 3-phosphate, and fructose 6-phosphate. The pathway can be described as eight distinct reactions (see below) and is separated into an oxidative phase and a non-oxidative phase. Reactions 1-3 form the oxidative phase and generate NADPH and pentose 5-phosphate. Reactions 4-8 form the non-oxidative phase and converts pentose 5-phosphate into other pentose sugars such as ribose 5-phosphate, but generates no NADPH. The eight reactions are as follows: reaction 1 where glucose-6-phosphate 1-dehydrogenase converts glucose 6-phosphate into D-glucono-1,5-lactone 6-phosphate with NADPH formation; reaction 2 where 6-phosphogluconolactonase converts D-glucono-1,5-lactone 6-phosphate into 6-phospho-D-gluconate;reaction 3 where 6-phosophogluconate dehydrogenase converts 6-phospho-D-gluconate into ribulose 5-phosphate with NADPH formation; reaction 4 where ribulose-phosphate 3-epimerase converts ribulose 5-phosphate into xylulose 5-phosphate; reaction 5 where ribose-5-phosphate isomerase converts ribulose 5-phosphate into ribose 5-phosphate; reaction 6 where transketolase rearranges ribose 5-phosphate and xylulose 5-phosphate to form sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate; reaction 7 where transaldolase rearranges of sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate to form erythrose 4-phosphate and fructose 6-phosphate; and reaction 8 where transkelotase rearranges of xylulose 5-phosphate and erythrose 4-phosphate to form glyceraldehyde 3-phosphate and fructose-6-phosphate.


Pw091899 View Pathway

Hop Pathway in Cardiac Development

The transcription of DNA is aided in large part by something called "homeodomain transcription factors". They are a diverse group of DNA binding factors. In fact, genes which are created with the aid of homeodomain factors tend to conglomerate and are responsible for anterior-posterior patterning. There is much to be said as well regarding the development and growth of cardiac myocytes and homedomain transcription factors. Indeed, at the early stages of the cell differentiation of cardiac myoctes a delicate balance of joint expression of several factors is needed for correct development (namely: serum response factor (SRF), and GATA4) and a homeodomain factor known as Nkx2-5! The joint expression of the aforementioned factors is the critical in the development of myocytes as well as gene expression in the cardiac region. To underline the importance of the homeodomain transcription factors, note that an error in the Nkx2-5 gene has severe consequences, which include, though are not necessarily limited to, embryonic lethality, as well as severe problems in general heart development. To put all this in context of the pathway in question, Hop actually stands for (Homeodomain Only Protein). The Hop gene plays an important role in the cardiac development we have been describing, as it too encodes a homedomain factor which plays an important role at the onset stages of cardiac development. The Hop gene is downstream of the Mkx2-5 factor we discussed earlier, and similar to it, improper activation of Hop can lead to severe cardiac development issues. In mice for example, not have the Hop gene results in alterations to the cell cycle. In particular, cardiac cells are unable to exit the cycle at the correct stage and continue grow after normal developmental stage has finished. There exists an interesting symbiosis between Hop and SRF. First, Hop regulates gene expression by either binding to SRF or by preventing SRF binding to DNA. This occurs because Hop does not have anything to bind to DNA with, and as such must have different methods to regulate gene expression. Second, when Hop blocks normal SRF binding, the results is that the activation of genes in the heart is affected and normal development does not occur. In a nutshell, what can be said about this tango action of SRF and Hop is this: during the first stages of development, what is observed is that the Hop interaction is one which results in a cessation of the differentiation processes which are induced by SRF. In the later stages, it appears that Hop reduces cell proliferation which is normally caused by SRF.


Pw000024 View Pathway

Folate Metabolism

Folate, or folic acid, is a very important B-vitamin involved in cell creation and preservation, as well as the protection of DNA from mutations that can cause cancer. It is commonly found in leafy green vegetables, but is also present in many other foods such as fruit, dairy products, eggs and meat. Folate is imperative during pregnancy as a deficiency will cause neural tube defects in the offspring. Many countries around the world now fortify foods with folic acid to prevent such defects. This pathway begins in the extracellular space, where folic acid is transported into the cell through a proton-coupled folate transporter. From there, dihydrofolate reductase converts folic acid into dihydrofolic acid. Dihydrofolic acid is then created into tetrahydrofolic acid through dihydrofolate reductase. Tetrahydrofolic acid then sparks the beginning of many reactions and subpathways including purine metabolism and histidine metabolism. There are two reactions that tetrahydrofolic acid undergoes, the first being the catalyzation into tetrahydrofolyl-[glu](2) through the enzyme folylpolyglutamate synthase in the mitochondria. Then, tetrahydrofolyl-[glu](2) becomes tetrahydrofolyl-[glu](n) through folylpolyglutamate synthase. The cycle ends with tetrahydrofolyl-[glu](n) reverting to tetrahydrofolyl-[glu](2) in the lysosome through the enzyme gamma-glutamyl hydrolase. The second reaction that begins with tetrahydrofolic acid sees tetrahydrofolic acid turned into 10-formyltetrahydrofolate through c-1-tetrahydrofolate synthase. This loop is completed by cytosolic 10-formyltetrahydrofolate dehydrogenase reverting 10-formyltetrahydrofolate back to tetrahydrofolic acid. Folate is not stored in the body for very long, as it is a water soluble vitamin and is excreted through urine, so it is important to ingest it continually, as your body’s level of folate will decline after a few weeks if the vitamin is avoided.


Pw000036 View Pathway

Thiamine Metabolism

Thiamine, (Vitamin B1), is a compound found in many different foods such as beans, seafood, meats and yogurt. It is usually maintained by the consumption of whole grains. It is an essential part of energy metabolism. This means that thiamine helps convert carbohydrates into energy. Eating carbohydrates increases the need for this vitamin, as your body can only store about 30mg at a time due to the vitamins short half-life. Thiamine was first synthesized in 1936, which was very helpful in researching its properties in relation to beriberi, a vitamin b1 deficiency. This deficiency has been observed mainly in countries where rice is the staple food. Thiamine metabolism begins in the extracellular space, being transported by a thiamine transporter into the cell. Once in the intracellular space, thiamine is converted into thiamine pyrophosphate through the enzyme thiamin pyrophosphate kinase 1. Thiamine pyrophosphate is then converted into thiamine triphosphate, again using the enzyme thiamin pyrophosphatekinase 1. After this, thiamine triphosphate uses thiamine-triphosphatase to revert to thiamine pyrophosphate, which undergoes a reaction using cancer-related nuceloside-triphosphatase to become thiamine monophosphate. This phosphorylated form is a metabolically active form of thiamine, as are the two other compounds, derivatives of thiamine, mentioned previously. The enzymes used in this pathway both stem from the upper small intestine. Thiamine is passed mainly through urine. It is a water-soluble vitamin, which means it dissolves in water and is carried to different parts of the body but is not stored in the body.


Pw000048 View Pathway

Phospholipid Biosynthesis

This pathway describes the synthesis of the common phospholipids, including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and cardiolipins. Phospholipid synthesis is mediated by two possible mechanisms: (1) A CDP-activated polar head group for attaches to the phosphate of phosphatidic acid or (2) A CDP-activated 1,2-diacylglycerol and an inactivated polar head group. The ER membrane is the primary site of phospholipid synthesis using precursors imported into the ER from the cytosol. To initiate the process, phosphatidic acid is generated by the linkage of two fatty acids associated with coenzyme A (CoA) carriers to glycerol-3-phosphate. This new molecule is inserted into the membrane where a phosphatase converts it into diacylglycerol or alternatively it is formed into phosphatidylinositol before the conversion. If the conversion into diacylglycerol occurs, the molecule has three possible fates depending on the type of polar head group attached: phosphatidylcholine, phosphatidylethanolamine, or phosphatidylserine. At their inception, a phospholipid is composed of a saturated fatty acid and unsaturated fatty acid on the C1 and C2 carbon of the glycerol backbone respectively. With the continuous remodelling of the phospholipid bilayer, this fatty acid distribution at these carbons changes. For example, acyl group remodelling changes the presence of acyl groups on the glycerol backbone (which were initially placed there by acyl transferases) and moves it further into the membrane as a consequence of the action of phospholipase A1 (PLA1) and phospholipase A2 (PLA2). Another modifying group that is usually added are alcohol-containing groups such as serine, ethanol amine, and choline which contain positively-charged nitrogen.


Pw000029 View Pathway

Lysine Degradation

The degradation of L-lysine happens in liver and it is consisted of seven reactions. L-Lysine is imported into liver through low affinity cationic amino acid transporter 2 (cationic amino acid transporter 2/SLC7A2). Afterwards, L-lysine is imported into mitochondria via mitochondrial ornithine transporter 2. L-Lysine can also be obtained from biotin metabolism. L-Lysine and oxoglutaric acid will be combined to form saccharopine by facilitation of mitochondrial alpha-aminoadipic semialdehyde synthase, and then, mitochondrial alpha-aminoadipic semialdehyde synthase will further breaks saccharopine down to allysine and glutamic acid. Allysine will be degraded to form aminoadipic acid through alpha-aminoadipic semialdehyde dehydrogenase. Oxoadipic acid is formed from catalyzation of mitochondrial kynurenine/alpha-aminoadipate aminotransferase on aminoadipic acid. Oxoadipic acid will be further catalyzed to form glutaryl-CoA, and glutaryl-CoA converts to crotonoyl-CoA, and crotonoyl-CoA transformed to 3-hydroxybutyryl-CoA. 3-Hydroxybutyryl-CoA will form Acetyl-CoA as the final product through the intermediate compound: acetoacetyl-CoA. Acetyl-CoA will undergo citric acid cycle metabolism. Carnitine is another key byproduct of lysine metabolism (not shown in this pathway).


Pw000043 View Pathway

Histidine Metabolism

Histidine, an amino acid, plays an important role in the creation of proteins. It is unique as an amino acid as it is needed for nucleotide formation. The biosynthesis of histidine in adults begins with the condensation of ATP and PRPP (phosphoribosyl pyrophosphate) to form n-5-phosphoribosyl 1-pyrophosphate (phosphoribosyl-ATP). It is also worth noting that PRPP is the beginning compound for purine and pyrimidine creation. Subsequent histidine biosynthetic steps (from phosphoribosyl-ATP onwards) are likely to occur in the intestinal microflora. Elimination of the phosphate and the opening of the ring in phosphoribosyl-ATP forms phosphoribosyl-forminino-5-aminoimidazole-4-carboxamide ribonucleotide(phosphoribosyl-forminino-AICAR-phosphate). This is subsequently converted to 5-phosphoribulosyl-forminino-5-aminoimidazole-4-carboxamide ribonucleotide. Cleavage of this compound creates imidazole glycerol phosphate and AICAR (aminoimidazolecarboxamide ribonucleotide) with glutamine being involved as an amino group donor. AICAR is used again through the purine pathway while the imidazole glycerol phosphate is converted to imidazole acetal phosphate. Transamination yields histidinol phosphate which is then turned into histidinol, and then, finally, to histidine. L-histidine is catalyzed by histidine ammonia-lyase into urocanic acid. This acid is then converted to 4-imidazolone-5-propionic acid by urocanate hydratase. 4-imidazolone-5-propionic acid is then converted to formiminoglutamic acid, using the enzyme probable imidazolonepropionase. One last reaction occurs to allow for glutamate metabolism, as formiminoglutamic acid is converted to l-glutamic acid through the use of formimidoyltransferase-cyclodeaminase. Histidine is also a precursor for carnosine biosynthesis(via carnosine synthase), with beta-alanine being the rate limiting precursor. Anserine can be synthesized either from carnosine via carnosine N-methyltransferase or from 1-methylhistidine via carnosine synthase. Inversely, cytosolic non-specific dipeptidase catalyzes the synthesis of 1-methylhistidine from anserine. Histidine is found in meat, seeds, nuts and whole grains. It is a very important amino acid in keeping a pH of 7 in the body, as it acts as a shuttle for protons to maintain a balance of acids and bases in the blood and different tissues.


Pw000163 View Pathway

Tryptophan Metabolism

This pathway depicts the metabolic reactions and pathways associated with tryptophan metabolism in animals. Tryptophan is an essential amino acid. This means that it cannot be synthesized by humans and other mammals and therefore must be part of the diet. Unlike animals, plants and microbes can synthesize tryptophan from shikimic acid or anthranilate. As one of the 20 proteogenic amino acids, tryptophan plays an important role in protein biosynthesis through the action of tryptophanyl-tRNA synthetase. As shown in this pathway, tryptophan can be linked to the tryptophanyl-tRNA via either the mitochondrial or cytoplasmic tryptophan tRNA ligases. Also shown in this pathway map is the conversion of tryptophan to serotonin (a neurotransmitter). In this process, tryptophan is acted upon by the enzyme tryptophan hydroxylase, which produces 5-hydroxytryptophan (5HTP). 5HTP is then converted into serotonin (5-HT) via aromatic amino acid decarboxylase. Serotonin, in turn, can be converted into N-acetyl serotonin (via serotonin-N-acetyltransferase) and then melatonin (a neurohormone), via 5-hydroxyindole-O-methyltransferase. The melatonin can be converted into 6-hydroxymelatonin via the action of cytochrome P450s in the endoplasmic reticulum. Serotonin has other fates as well. As depicted in this pathway it can be converted into N-methylserotonin via Indolethylamine-N-methyltransferase (INMT) or it can be converted into formyl-5-hydroxykynurenamine via indoleamine 2,3-dioxygenase. Serotonin may also be converted into 5-methoxyindoleacetate via a series of intermediates including 5-hydroxyindoleacetaldehyde and 5-hydroxyindoleacetic acid. Tryptophan can be converted or broken down into many other compounds as well. It can be converted into tryptamine via the action of aromatic amino acid decarboxylase. The resulting tryptamine can then be converted into indoleacetaldehyde via kynurenine 3-monooxygenase and then into indoleacetic acid via the action of aldehyde dehydrogenase. Tryptophan also leads to the production of a very important compound known as kynurenine. Kynurenine is synthesized via the action of tryptophan 2,3-dioxygnase, which produces N-formylkynurenine. This compound is converted into kynurenine via the enzyme known as kynurenine formamidase (AFMID). Kynurenine has at least 3 fates. First, kynurenine can undergo deamination in a standard transamination reaction yielding kynurenic acid. Secondly, kynurenine can undergo a series of catabolic reactions (involving kynureninase and kynurenine 3-monooxygenase) producing 3-hydroxyanthranilate plus alanine. In this reaction, kynureninase catabolizes the conversion of kynurenine into anthranilic acid while kynurenine—oxoglutarate transaminase (also known as kynurenine aminotransferase or glutamine transaminase K, GTK) catabolizes its conversion into kynurenic acid. The action of kynurenine 3-hydroxylase on kynurenic acid leads to 3-hydroxykynurenine. The oxidation of 3-hydroxyanthranilate converts it into 2-amino-3-carboxymuconic 6-semialdehyde, which has two fates. It can either degrade to form acetoacetate or it can cyclize to form quinolate. Most of the body’s 3-hydroxyanthranilate leads to the production of acetoacetate (a ketone body), which is why tryptophan is also known as a ketogenic amino acid. An important side reaction in the liver involves a non-enzymatic cyclization into quinolate followed by transamination and several rearrangements to yield limited amounts of nicotinic acid, which leads to the production of a small amount of NAD+ and NADP+.


Pw000151 View Pathway

Nicotinate and Nicotinamide Metabolism

Nicotinate (niacin) and nicotinamide - more commonly known as vitamin B3 - are precursors of the coenzymes nicotinamide-adenine dinucleotide (NAD+) and nicotinamide-adenine dinucleotide phosphate (NADP+). NAD+ synthesis occurs either de novo from amino acids, or a salvage pathway from nicotinamide. Most organisms use the de novo pathway whereas the savage pathway is only typically found in mammals. The specifics of the de novo pathway varies between organisms, but most begin by forming quinolinic acid (QA) from tryptophan (Trp) in animals, or aspartic acid in some bacteria (intestinal microflora) and plants. Nicotinate-nucleotide pyrophosphorylase converts QA into nicotinic acid mononucleotide (NaMN) by transfering a phosphoribose group. Nicotinamide mononucleotide adenylyltransferase then transfers an adenylate group to form nicotinic acid adenine dinucleotide (NaAD). Lastly, the nicotinic acid group is amidated to form a nicotinamide group, resulting in a molecule of nicotinamide adenine dinucleotide (NAD). Additionally, NAD can be phosphorylated to form NADP. The salvage pathway involves recycling nicotinamide and nicotinamide-containing molecules such as nicotinamide riboside. The precursors are fed into the NAD+ biosynthetic pathwaythrough adenylation and phosphoribosylation reactions. These compounds can be found in the diet, where the mixture of nicotinic acid and nicotinamide are called vitamin B3 or niacin. These compounds are also produced within the body when the nicotinamide group is released from NAD+ in ADP-ribose transfer reactions.
Showing 31 - 40 of 48701 pathways