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Glucose To Fructose Enzyme

High-fructose Corn Syrups (hfcs)

High-fructose Corn Syrups (hfcs)

With the development of glucoamylase in the 1940s and 1950s it became a straightforward matter to produce high DE glucose syrups. However, these have shortcomings as objects of commerce: D-glucose has only about 70% of the sweetness of sucrose, on a weight basis, and is comparatively insoluble. Batches of 97 DE glucose syrup at the final commercial concentration (71% (w/w)) must be kept warm to prevent crystallisation or diluted to concentrations that are microbiologically insecure. Fructose is 30% sweeter than sucrose, on a weight basis, and twice as soluble as glucose at low temperatures so a 50% conversion of glucose to fructose overcomes both problems giving a stable syrup that is as sweet as a sucrose solution of the same concentration (see Table 4.3 ). The isomerisation is possible by chemical means but not economical, giving tiny yields and many by-products (e.g. 0.1 M glucose 'isomerised' with 1.22 M KOH at 5C under nitrogen for 3.5 months gives a 5% yield of fructose but only 7% of the glucose remains unchanged, the majority being converted to various hydroxy acids). One of the triumphs of enzyme technology sofar has been the development of 'glucose isomerase'. Glucose is normallyisomerised to fructose during glycolysis but both sugars are phosphorylated. Theuse of this phosphohexose isomerase may be ruled out as a commercial enzymebecause of the cost of the ATP needed to activate the glucose and because twoother enzymes (hexokinase and fructose-6-phosphatase) would be needed tocomplete the conversion. Only an isomerase that would use underivatised glucoseas its substrate would be commercially useful but, until the late 1950s, theexistence of such an enzyme was not suspected. At about this time, enzymes werefound that catalyse the conversion of D-xylose to an Continue reading >>

What Enzymes Are Used To Break Down Carbohydrates

What Enzymes Are Used To Break Down Carbohydrates

What Enzymes Are Used to Break Down Carbohydrates The complex carbohydrates in whole-grain bread are broken down by enzymes during digestion. 4 What Enzymes Are Used to Break Down Carbohydrates? Carbohydrates, abundantly present in foods such as breads, cereals, fruits and vegetables, are the main source of energy in a diet. During digestion, a series of enzymatic reactions break down the carbohydrates in these foods into simple carbohydrates that are easily absorbed in the small intestine. While complex carbohydrates require enzymes such as salivary amylase, pancreatic amylase and maltose for digestion, simple carbohydrates require little or no enzymatic reaction before absorption. Different forms of carbohydrates are present in foods. Individual units of sugar such as glucose, fructose and galactose are the simplest forms of carbohydrates called monosaccharides, while sucrose, lactose and maltose are disaccharides made up of two monosaccharides linked together. Complex carbohydrates include starch and fiber, which are polysaccharides made up of long chains of glucose units bonded together. Although fiber resists enzyme action and is not broken down during digestion, break down of starch by enzymes starts in the mouth. Chewing breaks food into small molecules that combine with saliva secreted by the salivary glands in the mouth. Along with mucin and buffers, saliva contains the enzyme salivary amylase, which acts on the starch in food and breaks it down to maltose. Salivary amylase continues for the short duration that the carbohydrates are in the mouth, after which the mixture of the partially digested carbohydrates travels down the esophagus into the stomach. Due to the inhibition of salivary amylase activity by the acidic gastric juices, digestion of carbohydrates Continue reading >>

Reactor Design For The Enzymatic Isomerization Of Glucose To Fructose | Maria Zuiga - Academia.edu

Reactor Design For The Enzymatic Isomerization Of Glucose To Fructose | Maria Zuiga - Academia.edu

Reactor design for the enzymatic isomerization of glucose to fructose Bioprocess Engineering 7 (1992) 199-204 BioprocessEngineering 9 Springer-Verlag 1992Reactor design for the enzymatic isomerization of glucose to fructoseA. Illanes, M. E. Zfifiiga, S. Contreras, and A. Guerrero, Valparaiso, ChileAbstract. A comprehensive methodology is presented for the design so mole/m 3 bulk substrate concentrationof reactors using immobilized enzymes as catalysts. The design is s' mole/m 3 apparent substrate concentrationbased on material balances and rate equations for enzyme action T K temperatureand decay and considers the effect of mass transfer limitations on the t d timeexpression of enzyme activity. The enzymatic isomerization of glu- ti d operating time for reactor icose into fructose with a commercial immobilized glucose isomerase ts d time elapsed between two succes-was selected as a case study. Results obtained are consistent with sive charges of each reactordata obtained from existing high-fructose syrup plants. The method- V m 3 reactor volumenology may be extended to other cases, provided sound expressions v~ mole/m 3 s maximum apparent reaction ratefor enzyme action and decay are available and a simple flow pattern v~ mole/m a s maximum reaction rate for productwithin the reactor might be assumed. v~ m3 actual volume of catalyst bed v~ m3 calculated volume of catalyst bed v~ mol/m 3 s maximum reaction rate for sub-List of symbols strate V mol/m 3 s initial reaction rateC kat/kg specific activity of the catalyst vi m/s linear velocityD m2/s substrate diffusivity within the cata- vm mol/m 3 s apparent initial reaction rate lyst particle f(/q~, s', v,~)Dr m reactor diameter X substrate conversiond d operating time of each reactor Xeq substrate conversion at equilibrium Continue reading >>

Glucose-to-fructose Conversion At High Temperatures With Xylose (glucose) Isomerases From Streptomyces Murinus And Two Hyperthermophilic Thermotoga Species.

Glucose-to-fructose Conversion At High Temperatures With Xylose (glucose) Isomerases From Streptomyces Murinus And Two Hyperthermophilic Thermotoga Species.

Department of Chemical Engineering, North Carolina State University, Stinson Drive, Box 7905, Raleigh, North Carolina 27695-7905, USA. The conversion of glucose to fructose at elevated temperatures, as catalyzed by soluble and immobilized xylose (glucose) isomerases from the hyperthermophiles Thermotoga maritima (TMGI) and Thermotoga neapolitana 5068 (TNGI) and from the mesophile Streptomyces murinus (SMGI), was examined. At pH 7.0 in the presence of Mg(2+), the temperature optima for the three soluble enzymes were 85 degrees C (SMGI), 95 degrees to 100 degrees C (TNGI), and >100 degrees C (TMGI). Under certain conditions, soluble forms of the three enzymes exhibited an unusual, multiphasic inactivation behavior in which the decay rate slowed considerably after an initial rapid decline. However, the inactivation of the enzymes covalently immobilized to glass beads, monophasic in most cases, was characterized by a first-order decay rate intermediate between those of the initial rapid and slower phases for the soluble enzymes. Enzyme productivities for the three immobilized GIs were determined experimentally in the presence of Mg(2+). The highest productivities measured were 750 and 760 kg fructose per kilogram SMGI at 60 degrees C and 70 degrees C, respectively. The highest productivity for both TMGI and TNGI in the presence of Mg(2+) occurred at 70 degrees C, pH 7.0, with approximately 230 and 200 kg fructose per kilogram enzyme for TNGI and TMGI, respectively. At 80 degrees C and in the presence of Mg(2+), productivities for the three enzymes ranged from 31 to 273. A simple mathematical model, which accounted for thermal effects on kinetics, glucose-fructose equilibrium, and enzyme inactivation, was used to examine the potential for high-fructose corn syrup (HFCS) pro Continue reading >>

Ep2124640b1 - Glucose Isomerase For Use In The Treatment Of Fructose Intolerance - Google Patents

Ep2124640b1 - Glucose Isomerase For Use In The Treatment Of Fructose Intolerance - Google Patents

EP2124640B1 - Glucose isomerase for use in the treatment of fructose intolerance - Google Patents Glucose isomerase for use in the treatment of fructose intolerance EP2124640B1 EP20080707777 EP08707777A EP2124640B1 EP 2124640 B1 EP2124640 B1 EP 2124640B1 EP 20080707777 EP20080707777 EP 20080707777 EP 08707777 A EP08707777 A EP 08707777A EP 2124640 B1 EP2124640 B1 EP 2124640B1 Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.) Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.) Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.) A61MEDICAL OR VETERINARY SCIENCE; HYGIENE A61KPREPARATIONS FOR MEDICAL, DENTAL, OR TOILET PURPOSES A61K38/00Medicinal preparations containing peptides A61K38/16Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof A61K38/43Enzymes; Proenzymes; Derivatives thereof A23FOODS OR FOODSTUFFS; THEIR TREATMENT, NOT COVERED BY OTHER CLASSES A23LFOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL A23L29/00Foods or foodstuffs containing additives; Preparation or treatment thereof A23FOODS OR FOODSTUFFS; THEIR TREATMENT, NOT COVERED BY OTHER CLASSES A23LFOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A23B-A23J; TH

Glucose Isomerization By Enzymes And Chemo-catalysts: Status And Current Advances

Glucose Isomerization By Enzymes And Chemo-catalysts: Status And Current Advances

Glucose Isomerization by Enzymes and Chemo-catalysts: Status and Current Advances State-LocalJoint Engineering Laboratory for Comprehensive Utilization of Biomass,Center for R&D of Fine Chemicals, GuizhouUniversity, Guiyang 550025, PR China Centerof Innovative and Applied Bioprocessing (CIAB), Mohali 140 306, Punjab, India Centrefor Catalysis and Sustainable Chemistry, Department of Chemistry, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark Copyright 2017 American Chemical Society *E-mail: [email protected] ., *E-mail: [email protected] ; Tel.: +45 45252233. The well-known interconversion of aldoses to their corresponding ketoses was discovered more than a century ago, but has recently attracted renewed attention due to alternative application areas. Since the pioneering discovery, much work has been directed toward improving the process of isomerization of aldoses in terms of yields, catalysts, solvents, catalytic systems, etc., by both enzymatic and chemo-catalytic approaches. Among aldoseketose interconversion reactions, fructose production by glucose isomerization to make high-fructose corn syrup (HFCS) is an industrially important and large biocatalytic process today, and a large number of studies have been reported on the process development. In parallel, also alternative chemo-catalytic systems have emerged, as enzymatic conversion has drawbacks, though they are typically more selective and produce fructose under mild reaction conditions. Isomerization of glucose is also a central reaction for making renewable platform chemicals, such as lactic acid, 5-hydroxymethylfurfural (HMF), and levulinic acid. In these other applications, thermally stable catalysts are required, thus making use of enzymatic catalysis inadequate, since enzymes generally po Continue reading >>

Don't Waste Your Time And Money On A Fructose Breath Hydrogen Test

Don't Waste Your Time And Money On A Fructose Breath Hydrogen Test

Don't waste your time and money on a fructose breath hydrogen test Don't waste your time and money on a fructose breath hydrogen test In searching for why a child might have chronic bellyaches or other gastrointestinal symptoms, I often come across doctors ordering a test called a fructose breath hydrogen analysis. Every now and then, a parent seeks my advice about their childs test results. Although Ive never ordered the test myself, I decided to write this blog post to help answer the most common questions I get from parents. What does a fructose breath analysis test for? This test is done to determine whether someone is able to digest fructose normally. If the test is positive, then the child has fructose malabsorption. Fructose is a sugar (carbohydrate) molecule. When found in nature, fructose is what makes fruits, vegetables, honey, agave syrup, nectar, etc., sweet. Fructose also is also added to many packaged and processed foods as a flavoring agent and preservative. Fructose also is present in sucrose, the scientific term for the white powder we commonly refer to as sugar. Sucrose is considered a disaccharide because its formed when two separate molecules (glucose and fructose) are linked together. On their own, fructose and glucose are each monosaccharides. Starches, on the other hand, are polysaccharides, formed when multiple monosaccharides are linked together to form complex chains. Depending on the number of molecules found within a specific carbohydrate, our gut is designed to be able to digest it using a combination of enzymes and transporters. For instance, lactose (a disaccharide) is first digested by the enzyme lactase into one molecule of glucose and one molecule of galactose. Then each of these single molecules attaches to specific receptors found on Continue reading >>

Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar In Your Food

Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar In Your Food

Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food A Sugar Metabolism Kit containing most of the specialty supplies needed for this project is available from our partner Home Science Tools . Maple syrup on pancakes, ripe bananas, and soft drinks are all foods that are tasty to us because of the sugar in them. But did you know there are different kinds of sugar? One food can have multiple kinds of sugar in it, and our bodies actually process the different types of sugars differently. In this science project, you will measure the concentration of two sugarsglucose and sucrosein different foods, and investigate how sucrose is converted into glucose with the help of an enzyme called invertase. To investigate how an enzyme converts sucrose into glucose and how this changes the amount of glucose we digest from different foods. Yes, I Did This Project! Please log in (or create a free account) to let us know how things went. Are you planning to do a project from Science Buddies? Come back and tell us about your project using the I Did This Project link for the project you choose. Youll find a link to I Did This Project on every project on the Science Buddies website so dont forget to share your story! Andrew J. Bonham, PhD, Metropolitan State University of Denver Science Buddies Staff."Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food"Science Buddies.Science Buddies, 27 Oct. 2017.Web. 5 Apr. 2018

Fructose Malabsorption: A Beginners Guide To Treatment

Fructose Malabsorption: A Beginners Guide To Treatment

What is Fructose and Fructose Malabsorption? Fructose is a simple carbohydrate, or single sugar, found in many plants. Itsthe major sugar found in fruit, which is why its sometimes referred to as fruit sugar. However, it also occurs naturally in honey, wheat and some vegetables. As part of a fructan. Fructans are multiple fructose molecules joined to one glucose molecule. When fructose is eaten, it travels to the small intestine where it is absorbed without needing help from digestive enzymes. In fructose malabsorption , the left over fructose travels to the colon and takes lots of water with it (called an osmotic effect). Fructose is then fermented by gut bacteria in the colon (large intestine). This fermentation produces short chain fatty acids and the gases hydrogen, methane and carbon dioxide ( 1 ). Fructans are slightly different. They always travel straight to the colon where they are quickly fermented by bacteria. When fructans and other fructose are eaten together it may make symptoms worse ( 2 ). Summary: Fructose is a carbohydrate found in many plants. Fructose malabsorption causes fructose to move into the colon where it is fermented by bacteria, producing short chain fatty acids and gas. Fructose Malabsorption or Fructose Intolerance? You may hear fructose malabsorption and fructose intolerance used interchangeably, but they may not refer to the same thing. Fructose intolerance or hereditary fructose intolerance (HFI) is a genetic condition caused by deficiency of an enzyme that breaks down fructose in the liver. HFI is usually diagnosed at a young age, when babies start to eat food or have formula containing fructose ( 3 , 4 ). HFI can cause serious liver problems if left unmanaged. Fortunately, like fructose malabsorption, it can be effectively managed wi Continue reading >>

Office Of Science Outreach

Office Of Science Outreach

Part 2: The Molecular Biology and Biochemistry With modern high-throughput methods for determining the genes that particular tissues and organs express, it has been possible to look at gene-expression profiles in remarkable detail. From this, we learn that most organs express the gene for hexokinase, the first enzyme of energy metabolism. The liver does not. Instead, it expresses the genes for two different enzymes, glucokinase and fructokinase. This makes a big difference. First, a simplified summary of energy metabolism. First, most cells can metabolize sugars (e.g. glucose), fats (fatty acids), or amino acids. Part of the metabolism occurs in the cytoplasm, and part occurs in the mitochondria. In essence, cytoplasmic enzymes "prepare" sugars and fatty acids to enter mitochondria. Glucose is converted into pyruvate ("compound P" in the diagram on the right), and fatty acids are converted into Acetyl-CoA ("compound A" in the diagram). There is a shuttle system that can move Acetyl-CoA into mitochondria; in the diagram, think of the last part (Compound A complete metabolism) as the mitochondrial processes. Although it is not shown here, the function of all of this is to re-assemble ATP molecules that are used elsewhere in the cell. Amino acids can enter mitochondrial metabolism at different points, depending on the particular amino acid. In short, it is possible to use nearly anything as a source of energy. For a more detailed view of these biochemical reactions, click on the lefthand thumbnail on the right. The thumbnail to its right uses the purple highlight to illustrate the "flow" of glucose through these biochemical pathways. But different types of cells have different types of quirks. The three that are most important are these: Neurons (e.g. the brain and other Continue reading >>

Xylose Isomerase - Wikipedia

Xylose Isomerase - Wikipedia

D-Xylose isomerase tetramer from Streptomyces rubiginosus PDB 2glk . [1] One monomer is coloured by secondary structure to highlight the TIM barrel architecture. In enzymology , a xylose isomerase ( EC 5.3.1.5 ) is an enzyme that catalyzes the interconversion of D-xylose and D-xylulose . This enzyme belongs to the family of isomerases , specifically those intramolecular oxidoreductases interconverting aldoses and ketoses . The isomerase has now been observed in nearly a hundred species of bacteria. Xylose -isomerases are also commonly called fructose-isomerases due to their ability to interconvert glucose and fructose. The systematic name of this enzyme class is D-xylose aldose-ketose-isomerase. Other names in common use include D-xylose isomerase, D-xylose ketoisomerase, and D-xylose ketol-isomerase. The activity of D-xylose isomerase was first observed by Mitsuhashi and Lampen in 1953 in the bacterium Lactobacillus pentosus. [2] Artificial production through transformed E.coli have also been successful. [3] In 1957, the D-xylose isomerase activity on D-glucose conversion to D-fructose was noted by Kooi and Marshall. [4] It is now known that isomerases have broad substrate specificity. Most pentoses and some hexoses are all substrates for D-xylose isomerase. Some examples include: D-ribose, L-arabinose, L-rhanmose, and D-allose. [5] Conversion of glucose to fructose by xylose isomerase was first patented in the 1960s, however, the process was not industrially viable as the enzymes were suspended in solution, and recycling the enzyme was problematic. [5] An immobile xylose isomerase that was fixed on a solid surface was first developed in Japan by Takanashi. [5] These developments were essential to the development of industrial fermentation processes used in manufactur Continue reading >>

Brenda - Information On Ec 1.1.99.28 - Glucose-fructose Oxidoreductase

Brenda - Information On Ec 1.1.99.28 - Glucose-fructose Oxidoreductase

Information on EC 1.1.99.28 - glucose-fructose oxidoreductase for references in articles please use BRENDA:EC1.1.99.28 Please wait a moment until all data is loaded. This message will disappear when all data is loaded. Mark a special word or phrase in this record: Select one or more organisms in this record: The expected taxonomic range for this enzyme is: Bacteria, Eukaryota Please wait a moment until the data is sorted. This message will disappear when the data is sorted. Please wait a moment until the data is sorted. This message will disappear when the data is sorted. Please wait a moment until the data is sorted. This message will disappear when the data is sorted. D-glucose + D-fructose = D-gluconolactone + D-glucitol ping-pong mechanism with a single site for all substrates, two half-reactions with alternate reduction of NADP+ and oxidation of NADPH Please wait a moment until the data is sorted. This message will disappear when the data is sorted. Please wait a moment until the data is sorted. This message will disappear when the data is sorted. Please wait a moment until the data is sorted. This message will disappear when the data is sorted. D-mannose, D-xylose, D-galactose, 2-deoxy-D-glucose and L-arabinose will function as aldose substrates, but with low affinities. The ketose substrate must be in the open-chain form. The apparent affinity for fructose is low, because little of the fructose substrate is in the open-chain form. Xylulose and glycerone (dihydroxyacetone) will replace fructose, but they are poor substrates. The enzyme from Zymomonas mobilis contains tightly bound NADP+. Please wait a moment until the data is sorted. This message will disappear when the data is sorted. Please wait a moment until the data is sorted. This message will disappear whe Continue reading >>

Production Of Glucose And Fructose Syrups From Cassava (manihot Esculenta Crantz) Starch Using Enzymes Produced By Microorganisms Isolated From Brazilian Cerrado Soil

Production Of Glucose And Fructose Syrups From Cassava (manihot Esculenta Crantz) Starch Using Enzymes Produced By Microorganisms Isolated From Brazilian Cerrado Soil

Cinc. Tecnol. Aliment.vol.30no.1CampinasJan./Mar.2010 EpubMar05, 2010 Production of glucose and fructose syrups from cassava (Manihot esculenta Crantz) starch using enzymes produced by microorganisms isolated from Brazilian Cerrado soil Produo de xaropes de glicose e de fructose a partir de amido de mandioca (Manihot esculenta Crantz)usando enzimas produzidas por microorganismos isolados do solo de Cerrado Brasileiro Roberto do Nascimento SilvaI; Fbio Pereira QuintinoII; Valdirene Neves MonteiroIII; Eduardo Ramirez AsquieriII, * ILaboratrio de Enzimologia, Instituto de Cincias Biolgicas, Universidade Federal de Gois, CEP 74001-940, Goinia - GO, Brazil IILaboratrio de Tecnologia e Bioqumica de Alimentos, Faculdade de Farmcia, Universidade Federal de Gois, CEP 74001-940, Goinia - GO, Brazil, E-mail: [email protected] IIILaboratrio de Bioqumica de Microrganismos, Unidade Universitria de Cincias Exatas e Tecnolgicas da Universidade Estadual de Gois - UnUCET/UEG, BR 153, Km 98, Campus Henrique Santillo, CEP 75000-000, Anpolis - GO, Brazil The high demands for sugars and the development of enzymatic technology have increased the production of sweeteners, especially for glucose and fructose syrups. This work describe a technology for glucose and fructose syrups from Brazilian cassava starch using enzymes produced by soil microrganisms isolated from the Brazilian Cerrado soil. Firstly, Aspergillus niger and Streptomyces sp. were isolated from the soil and used as glucoamylase (GA) and glucose isomerase (GI) producer sources. After characterization, GA and GI exhibited optimum pH 4.5 and 8.0, respectively. GA showed maximum activity at 60 C and GI at 85 C. GA and GI retained 65 and 80%, respectively, of initial activity after 180 minutes of incubation at 60 C. The kinetic para Continue reading >>

Enzymes And Reaction Rates

Enzymes And Reaction Rates

Chemical reactions occur when molecules interact and chemical bonds between them are formed or broken. Some reactions will occur just by putting two substances in close proximity. For example, iron in the presence of oxygen will form iron oxide, or rust. Other reactions require energy to get the reaction started. Once the activation energy is added, the reaction will continue if the final energy state is lower than the initial energy state. A good example is a lightning strike that starts a forest fire which, once started, will continue to burn until the fuel is used up. In biology, chemical reactions are often aided by enzymes , biological molecules made of proteins which can be thought of as facilitators or catalysts . Enzymes speed the reaction, or allow it to occur at lower energy levels and, once the reaction is complete, they are again available. In other words, they are not used up by the reaction and can be re-used. Enzymes are designed to work most effectively at a specific temperature and pH. Outside of this zone, they are less effective. At very high temperatures, enzymes, because they are made of protein, can be denatured or destroyed. The material on which the enzyme will act is called the substrate . The enzyme attaches to the substrate molecule at a specific location called the active site . When the enzyme has attached to the substrate, the molecule is called the enzyme-substrate complex. For example, the sugar found in milk is called lactose. With the aid of the enzyme, lactase , the substrate, lactose, is broken down into two products, glucose and galactose. People who don't make enough lactase have trouble digesting milk products and are lactose intolerant . Children are usually lactose tolerant, but many people lose the ability to digest milk sugars Continue reading >>

Phase I: The Enzymes In Detail

Phase I: The Enzymes In Detail

Enzymes of Glycolysis The different enzymes involved in glycolysis act as kinases, mutases, and dehydrogenases, cleaving enzymes, isomerases or enolases. They act in concert to split or rearrange the intermediates, to add on phosphate groups, and to move those phosphate groups onto ADP to make ATP. Several of the reactions involve the phosphorylation of intermediates, which is important not only for the production of ATP from ADP, but also as a useful handle on the substrate for enzyme binding, to trap intermediates within the cell, and to drive pathways in one direction by making phosphorylation and dephosphorylation reactions irreversible. The different enzymes have been split into two groups, those in phase I and those in phase II, simply for convenience. Catalyses: a-D-Glucose + ATP à Glucose-6-phosphate (G6P) + ADP The first step in glycolysis is a priming reaction, where a phosphate group is added to glucose using ATP. This reaction is important for its ability to trap glucose within the cell. Whereas glucose can easily traverse the plasma membrane, the negatively charged phosphate group prevents G6P from crossing, so cells can stock up on glucose while levels are high. However, the hexokinase reaction is highly regulated, with G6P providing a feedback inhibition of the enzyme, thereby preventing excessive stockpiling until glycolysis depletes G6P levels. In mammals, there are four isozymes of hexokinase: types I, II, III and IV (glucokinase). These isozymes differ in their catalysis, localisation and regulation, thereby contributing to the different patterns of glucose metabolism in different tissues. Type I, II and III hexokinases can phosphorylate a variety of hexose sugars, including glucose, fructose and mannose, and as such are involved in a number of metab Continue reading >>

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