Is Fructose Substrate or Enzyme? 9 Facts (Read This First)

In this article we are focusing on the topic entitled as “Is Fructose Substrate or Enzyme? 9 Facts (Read This First)”. We are giving the detailed facts and explanations that supports our topic.

Fructose is a substrate for many biochemical reactions occurring inside the living cells regularly. The metabolism of fructose inside the cells is called “Fructolysis” and the metabolism of glucose is referred to as Glycolysis. The enzymes and intermediate structures that are involved in glycolysis are common in fructolysis but the site and the metabolic fate of both sugars is entirely different.

Fructose is a type of sugar and has been classified as a monosaccharide with glucose. Fructose is present in dietary foods and is naturally found in vegetables and fruits. The site of metabolism for glucose and fructose are different, glucose is metabolized in the entire body while the metabolism of fructose entirely occurs in the liver in humans. In the liver fructose is used as a substrate for the synthesis of glycogen and triglycerides.

Structure of Fructose

Fructose is a monosaccharide found in plants. Glucose and fructose together form a disaccharide called sucrose. Fructose structure is made up of basic atoms, like, carbon, hydrogen and oxygen and the chemical formula of fructose can be written as C6H12O6.

Fructose in its pure crystalline form is white powdery, sweet in taste, odorless and is water soluble. The common sources of fructose include, flowers, fruits, honey, trees, rooted vegetables and berries.

is fructose substrate
Structure of beta-D-fructofuranose Image from Wikipedia

Function of Fructose

The main function of fructose is that it enhances the metabolism of glucose and also facilitates the proper absorption and removal of loads for carbohydrates taken through diet. In liver fructose is converted into the glucose first before its absorption by the cells. In the body, glucose is the prime source of energy to regulate and carry out the normal functioning of the cells.

At times fructose is also used as an alternative metabolite by the cells in order to generate required energy when glucose is not present in the sufficient amount and the energy demand for metabolic processes is high.

is fructose substrate
Isomeric forms of Fructose Image from Wikipedia

Benefits of Fructose

Fructose is a monosaccharide sugar and is beneficial in lot of ways. Some of the benefits are mentioned below:

  • Fructose is the energy source of the body and it also increases the body’s CO2.
  • It helps in the metabolism of glucose.
  • It maintains the metabolism during calorie deficient conditions.
  • Fructose boosts the endurance during intense exercise.
  • Fructose helps in proper digestion of dairy products usually taken in diet which normally contains carbohydrates.
  • Fructose plays an important role in improving the digestion in liver cells and helps in its functioning to go smoothly.
  • The glycemic index of fructose is very low and has been advised to be consumed as an alternative sweetener for diabetic patients.
  • Fructose is used in industries as a sweetener in the production of baked products, soft drinks and many other food materials.

Side effects of Fructose

Consuming excess amount of fructose in diet has been proven to cause various detrimental side effects in the body. Some of the side effects for increased fructose consumption are below;

  • Fructose malabsorption: fructose malabsorption has been studied to be the possible cause for functional bowel disorder and other gastrointestinal disorders such as irritable bowel disorder, recurrent abdominal pain, diarrhea, etc.
  • Increase in the level of fructose can lead to the depletion of ATP in the cells and can also cause an increase in uric acid production.
  • Chronic metabolic liver disorders: consuming a high amount of fructose can be a greater risk for nonalcoholic fatty liver abnormalities (NAFLD) and non-alcoholic steatohepatitis (NASH).
  • Excess fructose can alter the lipid composition in the blood and can also raise VLDL cholesterol levels that leads to the accumulation of fat in organs and arteries which becomes a potential cause of heart abnormalities including high blood pressure, heart failure, etc.

When is fructose substrate?

Fructose acts as a poor substrate for the enzyme called glucokinase which catalyzes the addition of a phosphate group to glucose and convert it into glucose-6-phosphate. Glucokinase is active mostly in the liver cells. The metabolism of fructose takes place in liver. It is used for the synthesis of fats inside liver. Fructose act as a substrate during the metabolism of glucose.

Fructose Metabolism
Metabolism of Fructose Image from Wikipedia

How is fructose substrate?

Fructose is widely distributed monosaccharide and is found in almost all vegetables and fruits. Fructose is known to be a poor substrate for the enzyme called glucokinase. Fructose acts as a potential substrate in all metabolic pathways that involves carbon metabolism, which involves, glycolysis, oxidative phosphorylation, glycogenesis, lipogenesis, etc.

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Conversion of Sucrose to Glucose and Fructose Image from Wikipedia

Why is fructose substrate?

Fructose is delivered and metabolized in liver for the production of energy and carbon precursor to avoid the dependence on insulin.  Fructose transport and metabolism does not require insulin. Metabolism of fructose is necessary to happen inside body. Fructose is a substrate for glucokinase enzyme.

The sites of metabolism for fructose are, liver, kidney, intestine, muscles and adipose tissue. The metabolism of glucose and fructose is quite similar. The process of energy production at the end of fructose metabolism is known as fructolysis.

Where fructose is found?

Fructose is a simple sugar which has been classified as monosaccharide and is found widely in nature. Fructose is present in fruits, vegetables, honey, trees, etc. Common sources of fructose are as follows;

  • Fruits: Dates, raisins, cherries, figs, watermelon, dates, plums, apricots, jackfruit, grapes, tangerines, raspberries, pineapple, peaches, lemon juice, apricots, cranberries, papaya, blueberries, bananas, mangoes, kiwi, apples, etc.
  • Vegetables: Jalapeno, cauliflower, squash, onions, cucumber, corn, radishes, eggplant, cabbage, sweet potato, carrots, okra, celery, potato, beans, tomatoes, turnip, spinach, lettuce, peppers, mushrooms, asparagus, etc.
  • Condiments: Honey, sauce, tomato pastes, barbecue sauce, etc.
  • Wheat based products: bread, cereals, cakes, cookies, crackers, noodles, pastries, etc.
  • Drinks: fruit juices, wines, sweetened soft drinks.

Why fructose is not an Enzyme?

Fructose is a type of carbohydrate which has been classified as a monosaccharide. Fructose is a substrate for the enzyme called glucokinase. The metabolism of fructose in liver is enzyme based and the enzymes which are known to participate in this process of metabolism of fructose are, fructokinase, fructose-bisphosphate aldolase B and adenosine triphosphate and ATP dependent dihydroxyacetone kinase. These enzymes are found in liver, kidneys and intestine. 

How fructose is produced?

Fructose is a naturally occurring sugar which is found in plants and vegetables. Fructose and glucose together form a disaccharide sugar called sucrose. In endogenous fructose production glucose, mannose, xylose is isomerized to obtain fructose. Fructose is also produced by the dehydrogenation of sorbitol.

Fructose is produced by the breakdown of sucrose with glucose. Sucrase is the enzyme that catalysis the splitting of sucrose into glucose and fructose. In green plants, sugars are formed during the process of photosynthesis which include glucose and fructose.

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Fructose Transport Image from Wikipedia


To conclude the article, we can say that fructose is a substrate and is used as an energy source in the cell to perform various metabolic processes and biochemical reactions, fructose is produced naturally in plants and vegetables.

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