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Why Is Fructose Metabolized More Quickly Than Glucose In Hepatocytes

Glucose & Fructose Metabolism

Glucose & Fructose Metabolism

Glucose and fructose are simple sugars that have the same chemical formula with a different structural arrangement of the atoms. Glucose is a source of energy for all of your tissues, and can be stored by the body for energy upon demand. It's also used to make other sugars needed in your genetic material and connective tissues. Fructose is primarily metabolized in your liver, and excesses are used to make body fat. Glycolysis is the initial process in the harvesting of energy from glucose. After glucose enters your tissue cells, an enzyme called phosphofructokinase determines whether or not glucose will be used for energy. If your cell needs energy, phosphofructokinase will allow glycolysis to proceed. If your cell is well-supplied with oxygen, glucose will be completely burned for energy, which is called aerobic glycolysis. If oxygen is in short supply, glucose will only be partially burned and then converted into lactic acid. This is called anaerobic glycolysis and it occurs when your muscles are working hard but not getting enough oxygen. Glycogen If glucose enters your cells and is not immediately needed for energy, glucose molecules can be linked together in branching chains and stored as a form of starch called glycogen. When energy is needed, glycogen can be broken down into glucose. Your muscles store glycogen for their own use. However, your liver can store large amounts of glucose as glycogen, and if your blood glucose level gets too low, glycogen can be broken down into glucose and released into your blood for use by other tissues. Gluconeogenesis When your blood glucose level falls too low, your liver can also make glucose from non-glucose sources and then secrete the glucose into your blood for other tissues to use for energy. This process is called glucone Continue reading >>

Enzymes Of Fructose Metabolism In Human Liver

Enzymes Of Fructose Metabolism In Human Liver

Enzymes of fructose metabolism in human liver This article has been cited by other articles in PMC. The enzyme activities involved in fructose metabolism were measured in samples of human liver. On the basis of U/g of wet-weight the following results were found: ketohexokinase, 1.23; aldolase (substrate, fructose-1-phosphate), 2.08; aldolase (substrate, fructose-1,6-diphosphate), 3.46; triokinase, 2.07; aldehyde dehydrogenase (substrate, D-glyceraldehyde), 1.04; D-glycerate kinase, 0.13; alcohol dehydrogenase (nicotinamide adenine dinucleotide [NAD]) substrate, D-glyceraldehyde), 3.1; alcohol dehydrogenase (nicotinamide adenine dinucleotide phosphate [NADP]) (substrate, D-glyceraldehyde), 3.6; and glycerol kinase, 0.62. Sorbitol dehydrogenases (25.0 U/g), hexosediphosphatase (4.06 U/g), hexokinase (0.23 U/g), and glucokinase (0.08 U/g) were also measured. Comparing these results with those of the rat liver it becomes clear that the activities of alcohol dehydrogenases (NAD and NADP) in rat liver are higher than those in human liver, and that the values of ketohexokinase, sorbitol dehydrogenases, and hexosediphosphatase in human liver are lower than those values found in rat liver. Human liver contains only traces of glycerate kinase. The rate of fructose uptake from the blood, as described by other investigators, can be based on the activity of ketohexokinase reported in the present paper. In human liver, ketohexokinase is present in a four-fold activity of glucokinase and hexokinase. This result may explain the well-known fact that fructose is metabolized faster than glucose. Full text is available as a scanned copy of the original print version. Get a printable copy (PDF file) of the complete article (814K), or click on a page image below to browse page by page. Link Continue reading >>

Enzymes Of Fructose Metabolism In Human Liver

Enzymes Of Fructose Metabolism In Human Liver

The enzyme activities involved in fructose metabolism were measured in samples of human liver. On the basis of U/g of wet-weight the following results were found: ketohexokinase, 1.23; aldolase (substrate, fructose-1-phosphate), 2.08; aldolase (substrate, fructose-1,6-diphosphate), 3.46; triokinase, 2.07; aldehyde dehydrogenase (substrate, D-glyceraldehyde), 1.04; D-glycerate kinase, 0.13; alcohol dehydrogenase (nicotinamide adenine dinucleotide [NAD]) substrate, D-glyceraldehyde), 3.1; alcohol dehydrogenase (nicotinamide adenine dinucleotide phosphate [NADP]) (substrate, D-glyceraldehyde), 3.6; and glycerol kinase, 0.62. Sorbitol dehydrogenases (25.0 U/g), hexosediphosphatase (4.06 U/g), hexokinase (0.23 U/g), and glucokinase (0.08 U/g) were also measured. Comparing these results with those of the rat liver it becomes clear that the activities of alcohol dehydrogenases (NAD and NADP) in rat liver are higher than those in human liver, and that the values of ketohexokinase, sorbitol dehydrogenases, and hexosediphosphatase in human liver are lower than those values found in rat liver. Human liver contains only traces of glycerate kinase. The rate of fructose uptake from the blood, as described by other investigators, can be based on the activity of ketohexokinase reported in the present paper. In human liver, ketohexokinase is present in a four-fold activity of glucokinase and hexokinase. This result may explain the well-known fact that fructose is metabolized faster than glucose. Do you want to read the rest of this article? ... Using positional isotope-labeled fructose, we show that glycerate is made selectively from fructose carbons 4, 5, 6. This makes biochemical sense, as the canonical fructose catabolic pathway converts these carbons into glyceraldehyde, whose oxid Continue reading >>

Fructose Metabolism And Health Risks

Fructose Metabolism And Health Risks

Fructose is a monosaccharide mainly found in fruits , vegetables and honey [ 1 ]. It has been commonly consumed in human diet, however the daily intake has increased in the past 40 years due to its industrial production [ 2 ]. High fructose corn syrup (HFCS), also called glucose or fructose syrup, is used as a sweetener in many products such as sweets, cakes and drinks. Consumption of fructose as a single nutrient is rare and its absorption decreases due to high fiber content of its natural sources. Chemical structures of glucose and fructose are presented in Figure 1. The main source of fructose in human diet is sucrose or HFCS that is composed of fructose and glucose in different ratios such as HFCS 55 indicating 55% fructose [ 1 , 2 ]. These sweeteners are preferred in food industry because they are much cheaper and have better functional characteristics. In recent years, there has been a parallel increase in dietary exposure to fructose as well as in the incidences of metabolic diseases . This leads to the idea that consumption of high fructose may have a negative impact on human health. In a number of scientific reports, dietary fructose has been implicated in several diseases. In a study carried out with young men and women, high fructose corn syrup was reported to increase postprandial triglycerides, LDL cholesterol, and Apolipoprotein-B which are indicators of cardiovascular disease risk factors [ 3 ]. In a cross-sectional analysis of the data collected from the National Health and Nutrition Examination Survey NHANES from 2003 to 2006, high fructose intake was determined to be significantly associated with elevated blood pressure levels [ 4 ]. Recent literature survey based on article search in scientific databases including PubMed after the year 2000, high fru Continue reading >>

Fructose Metabolism More Complicated Than Was Thought

Fructose Metabolism More Complicated Than Was Thought

Follow all of ScienceDaily's latest research news and top science headlines ! Fructose Metabolism More Complicated Than Was Thought University of Illinois at Urbana-Champaign A new study suggests that we may pay a price for ingesting too much fructose. Chances are you consume quite a bit of fructose. Most Americans do --- in refined sugars such as sucrose or table sugar (which is half fructose) and in high-fructose corn syrup, used in products as diverse as soft drinks, protein bars, and fruit juice. Dietary fructose affects a wide range of genes in the liver that had not previously been identified. Chances are you consume quite a bit of fructose. Most Americans do --- in refined sugars such as sucrose or table sugar and in high-fructose corn syrup, used in products as diverse as soft drinks, protein bars, and fruit juice. Chances are you consume quite a bit of fructose. Most Americans do --- in refined sugars such as sucrose or table sugar and in high-fructose corn syrup, used in products as diverse as soft drinks, protein bars, and fruit juice. A new University of Illinois study suggests that we may pay a price for ingesting too much fructose. According to lead author Manabu Nakamura, dietary fructose affects a wide range of genes in the liver that had not previously been identified. Chances are you consume quite a bit of fructose. Most Americans doin refined sugars such as sucrose or table sugar (which is half fructose) and in high-fructose corn syrup, used in products as diverse as soft drinks, protein bars, and fruit juice. But many scientists believe that high dietary fructose contributes to the development of metabolic syndrome, a group of risk factors that predict heart disease and Type 2 diabetes. "For this reason, it's important for scientists to understand e Continue reading >>

Fructose & Liver Metabolism

Fructose & Liver Metabolism

All carbohydrates, such as fruit, vegetables and baked goods, are made up of simple sugars called monosaccharides. Fructose is a type of monosaccharide found in most carbohydrates, although its naturally most abundant in fruit. It's also artificially added to many commercially produced foods and beverages in the form of high fructose corn syrup. Fructose, also called fruit sugar, is metabolized in your liver and has a different effect on your body than other sugars. Fructose is one of three simple sugars, along with glucose and galactose, which are absorbed directly into your bloodstream during the process of digestion in your small intestine. Fructose exists freely in most plant-based foods, although its also a component of a more complex sugar called sucrose, which is used for common table sugar. Sucrose must be broken down into fructose and glucose before the simple sugars are absorbed. Once absorbed through the intestine, fructose is transported to the liver via the hepatic portal vein for metabolism. In contrast, glucose typically passes right through the liver and is delivered directly to all the cells of your body for metabolism and energy production. Thats why glucose is called blood sugar. Once in the liver, fructose is chemically changed by the enzymes fructokinase, aldolase B and triokinase. The end-product of fructose metabolism in the liver is a substance that can either become glucose, glycogen, fat or pyruvate, which is the end-product of glucose metabolism. In essence, fructose is a fairly versatile type of fuel that your body can use right away in the liver, store for later use as glycogen and fat, or send it on to other tissues as glucose. Glycogen is stored in the liver and muscles and serves as the secondary long-term energy source for your body. Th Continue reading >>

Spotlight On Sugar

Spotlight On Sugar

We encounter sugar in two different ways in our food: sugars that exist in unprocessed foods such as fruits, vegetables, and dairy products, and sugars that are added to packaged foods to boost flavor or allow food to be more shelf-stable. Added sugars are not chemically different from naturally occurring sugars. Both are broken down in the body using the same enzymatic processes. However, the amount and form in which we consume the sugars—in fruits and vegetables, in sodas, or in other processed foods—affects how quickly the body absorbs them, and how the body signals and experiences satiety, or feelings of fullness. Digestible carbohydrates, including “complex” starches and “simple” sugars, are all nutritionally similar in that they each provide 4 calories per gram. They are also chemically similar: more-complex carbohydrates have to be broken into simple sugars before they can be absorbed, transported by the bloodstream, and used for energy. Carbohydrate breakdown takes place high in the digestive tract, and with high efficiency. Starch is broken into glucose units and absorbed at about the same rate as pure glucose. Likewise, sucrose (a disaccharide made up of glucose paired with fructose) is clipped apart and absorbed about as quickly as high fructose corn syrup (a mixture of individual glucose and fructose units). Glucose and fructose have the same chemical formula: C6H12O6. But the atoms are arranged differently, giving the two sugars different chemical properties. The chemical structures of fructose and glucose influence their sweetness and how they are processed in the body. Sweetness Fructose tastes twice as sweet as glucose, and sucrose (composed of fructose and glucose linked together) is somewhere in between. The proportion of these sugars in fo 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 >>

Fructolysis - Wikipedia

Fructolysis - Wikipedia

This article has multiple issues. Please help improve it or discuss these issues on the talk page . This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed. This article possibly contains original research . Please improve it by verifying the claims made and adding inline citations . Statements consisting only of original research should be removed. ( Learn how and when to remove this template message ) Fructolysis refers to the metabolism of fructose from dietary sources. Though the metabolism of glucose through glycolysis uses many of the same enzymes and intermediate structures as those in fructolysis, the two sugars have very different metabolic fates in human metabolism. Unlike glucose, which is metabolized widely in the body, fructose is metabolized almost completely in the liver in humans, where it is directed toward replenishment of liver glycogen and triglyceride synthesis. [1] Under one percent of ingested fructose is directly converted to plasma triglyceride. [2] 29% - 54% of fructose is converted in liver to glucose, and about quarter of fructose is converted to lactate . 15% - 18% is converted to glycogen . [3] Glucose and lactate are then used normally as energy to fuel cells all over the body. [2] Fructose is a dietary monosaccharide present naturally in fruits and vegetables , either as free fructose or as part of the disaccharide sucrose , and as its polymer inulin . It is also present in the form of refined sugars including granulated sugars (white crystalline table sugar, brown sugar , confectioner's sugar , and turbinado sugar ), refined crystalline fructose and as high fructose corn syrups . About 10% of the calories contai Continue reading >>

Differential Effects Of Central Fructose And Glucose On Hypothalamic Malonylcoa And Food Intake

Differential Effects Of Central Fructose And Glucose On Hypothalamic Malonylcoa And Food Intake

Differential effects of central fructose and glucose on hypothalamic malonylCoA and food intake Seung Hun Cha, Michael Wolfgang, Yuka Tokutake, Shigeru Chohnan and M. Daniel Lane PNAS November 4, 2008. 105 (44) 16871-16875; The American diet, especially that of adolescents, contains highly palatable foods of high-energy content and large amounts of high-fructose sweeteners. These factors are believed to contribute to the obesity epidemic and insulin resistance. Previous investigations revealed that the central metabolism of glucose suppresses food intake mediated by the hypothalamic AMP-kinase/malonylCoA signaling system. Unlike glucose, centrally administered fructose increases food intake. Evidence presented herein indicates that the more rapid initial steps of central fructose metabolism deplete hypothalamic ATP level, whereas the slower regulated steps of glucose metabolism elevate hypothalamic ATP level. Consistent with effects on the [ATP]/[AMP] ratio, fructose increases phosphorylation/activation of hypothalamic AMP kinase causing phosphorylation/inactivation of acetylCoA carboxylase, whereas glucose has the inverse effects. The changes provoked by central fructose administration reduce hypothalamic malonylCoA level and thereby increase food intake. These findings explain the paradoxical fructose effect on food intake and lend credence to the malonylCoA hypothesis. Over the past three decades there has been an alarming increase in the incidence of obesity and type 2 diabetes in the United States ( 1 ). Particularly troubling is the rise of these conditions in youth ( 2 ). Paralleling this rise has been the extensive use of high-fructose sweeteners in the diet and increasing evidence that fructose may be a contributing factor to the obesity epidemic ( 3 ). These Continue reading >>

Fructose - An Overview | Sciencedirect Topics

Fructose - An Overview | Sciencedirect Topics

Fructose is a 6-carbon ketose found in fruit and honey as a monosaccharide, and in sucrose (a disaccharide of fructose and glucose). J.M. Johnson, F.D. Conforti, in Encyclopedia of Food Sciences and Nutrition (Second Edition) , 2003 Fructose is a monosaccharide. Fructose bonded with glucose, another monosaccharide, forms sucrose, or table sugar. Fructose also occurs naturally in abundance in fruits (Table 1) and in lesser amounts in tuberous vegetables such as onions and potatoes. These sources alone contribute some 4060% of an individual's total fructose intake. However, the major source of fructose as an ingredient in food is from the hydrolyzation of starch to glucose, which is then converted to fructose. (See CARBOHYDRATES | Classification and Properties.) Fruits are a rich source of mono- and disaccharides. Dates contain up to 48.5% sucrose, and dried figs contain a mixture of 30.9% fructose and 42.0% glucose. The sucrose content of most fruit and fruit juices is low, though some varieties of melons, peaches, pineapple, and tangerine contain 69% sucrose, and mango contains 11.6% sucrose. Reducing sugars (primarily a mixture of fructose and glucose) are the main soluble carbohydrate of most fruits and account for 70% of seedless raisins. Vegetables contain substantially less fructose and glucose than fruits, and the only significant source of sucrose is sugar beets. In the late 19th century corn or potato starch was hydrolyzed with dilute acid to yield glucose and dextrins for commercial purposes. In the 1940s, cornstarch was the primary choice for the production of glucose and the introduction of enzyme technology for hydrolysis reactions contributed to the development of glucose syrups to fructose syrups of specified glucose content. The conversion of glucose syr Continue reading >>

Fructose Metabolism: Relation To Food Intake & Metabolic Dysfunction

Fructose Metabolism: Relation To Food Intake & Metabolic Dysfunction

Diets containing large amounts of sucrose (a disaccharide of glucose and fructose) can utilize the fructose as a major source of energy. It should be pointed out that the difference between the amount of fructose available from sucrose obtained from cane or beet sugars is not significantly less than that from corn syrup. Corn syrup is somewhat improperly identified as high fructose corn syrup (HFCS) giving the impression that it contains a large amount of fructose. However, whereas the fructose content of sucrose is 50% (since it is a pure disaccharide of only glucose and fructose), the content in HFCS is only 55%. The reason HFCS has more than 50% fructose is because the glucose extracted from corn starch is enzymatically treated to convert some of the glucose to fructose. This is done in order to make the sugar sweeter which is why it is particularly popular in the food industry. Therefore, any disorder and/or dysfunction (see below), attributed to the consumption of fructose, can be manifest whether one consumes cane or beet sugar or HFCS. The pathway to utilization of fructose differs in muscle and liver due to the differential distribution of fructose phosphorylating enzymes. Hexokinases are a family of enzymes that phosphorylate hexose sugars such as glucose. Four mammalian isozymes of hexokinase are known (Types IIV), with the Type IV isozyme often referred to as glucokinase. Glucokinase is the form of the enzyme found in hepatocytes and pancreatic -cells. Several of the hexokinases (but not type IV) can phosphorylate various different hexoses including fructose. In addition to hexokinases, fructose can be phosphorylated by fructokinases. Fructokinases are formally referred to as ketohexokinases (KHK). There are two forms of KHK in mammals that result from alter Continue reading >>

Fructose In Perspective

Fructose In Perspective

Feinman and Fine; licensee BioMed Central Ltd.2013 Whether dietary fructose (as sucrose or high fructose corn syrup) has unique effects separate from its role as carbohydrate, or, in fact, whether it can be considered inherently harmful, even a toxin, has assumed prominence in nutrition. Much of the popular and scientific media have already decided against fructose and calls for regulation and taxation come from many quarters. There are conflicting data, however. Outcomes attributed to fructose obesity, high triglycerides and other features of metabolic syndrome are not found in every experimental test and may be more reliably caused by increased total carbohydrate. In this review, we try to put fructose in perspective by looking at the basic metabolic reactions. We conclude that fructose is best understood as part of carbohydrate metabolism. The pathways of fructose and glucose metabolism converge at the level of the triose-phosphates and, therefore, any downstream effects also occur with glucose. In addition, a substantial part of ingested fructose is turned to glucose. Regulation of fructose metabolism per se, is at the level of substrate control the lower Km of fructokinase compared to glucokinase will affect the population of triose-phosphates. Generally deleterious effects of administering fructose alone suggest that fructose metabolism is normally controlled in part by glucose. Because the mechanisms of fructose effects are largely those of a carbohydrate, one has to ask what the proper control should be for experiments that compare fructose to glucose. In fact, there is a large literature showing benefits in replacing total carbohydrate with other nutrients, usually fat, and such experiments sensibly constitute the proper control for comparisons of the two suga Continue reading >>

Jci -enzymes Of Fructose Metabolism In Human Liver

Jci -enzymes Of Fructose Metabolism In Human Liver

Enzymes of fructose metabolism in human liver Fritz Heinz, , Walther Lamprecht, Joachim Kirsch J Clin Invest. 1968; 47(8) :1826-1832. . The enzyme activities involved in fructose metabolism were measured in samples of human liver. On the basis of U/g of wet-weight the following results were found: ketohexokinase, 1.23; aldolase (substrate, fructose-1-phosphate), 2.08; aldolase (substrate, fructose-1,6-diphosphate), 3.46; triokinase, 2.07; aldehyde dehydrogenase (substrate, D-glyceraldehyde), 1.04; D-glycerate kinase, 0.13; alcohol dehydrogenase (nicotinamide adenine dinucleotide [NAD]) substrate, D-glyceraldehyde), 3.1; alcohol dehydrogenase (nicotinamide adenine dinucleotide phosphate [NADP]) (substrate, D-glyceraldehyde), 3.6; and glycerol kinase, 0.62. Sorbitol dehydrogenases (25.0 U/g), hexosediphosphatase (4.06 U/g), hexokinase (0.23 U/g), and glucokinase (0.08 U/g) were also measured. Comparing these results with those of the rat liver it becomes clear that the activities of alcohol dehydrogenases (NAD and NADP) in rat liver are higher than those in human liver, and that the values of ketohexokinase, sorbitol dehydrogenases, and hexosediphosphatase in human liver are lower than those values found in rat liver. Human liver contains only traces of glycerate kinase. The rate of fructose uptake from the blood, as described by other investigators, can be based on the activity of ketohexokinase reported in the present paper. In human liver, ketohexokinase is present in a four-fold activity of glucokinase and hexokinase. This result may explain the well-known fact that fructose is metabolized faster than glucose. Continue reading >>

Fructose Metabolism And Relation To Atherosclerosis, Type 2 Diabetes, And Obesity

Fructose Metabolism And Relation To Atherosclerosis, Type 2 Diabetes, And Obesity

Journal of Nutrition and Metabolism Volume 2015 (2015), Article ID 823081, 12 pages 1Faculty of Public Health, Hedmark University College, P.O. Box 400, 2418 Elverum, Norway 2Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway Academic Editor: Michael B. Zemel Copyright © 2015 Astrid Kolderup and Birger Svihus. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A high intake of sugars has been linked to diet-induced health problems. The fructose content in sugars consumed may also affect health, although the extent to which fructose has a particularly significant negative impact on health remains controversial. The aim of this narrative review is to describe the body’s fructose management and to discuss the role of fructose as a risk factor for atherosclerosis, type 2 diabetes, and obesity. Despite some positive effects of fructose, such as high relative sweetness, high thermogenic effect, and low glycaemic index, a high intake of fructose, particularly when combined with glucose, can, to a larger extent than a similar glucose intake, lead to metabolic changes in the liver. Increased de novo lipogenesis (DNL), and thus altered blood lipid profile, seems to be the most prominent change. More studies with realistic consumption levels of fructose are needed, but current literature does not indicate that a normal consumption of fructose (approximately 50–60 g/day) increases the risk of atherosclerosis, type 2 diabetes, or obesity more than consumption of other sugars. However, a high intake of fructose, particularly if combined with a high energy intake in the form of glucose/starch, ma Continue reading >>

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