What Enzyme Turns Sucrose Into Glucose? Unraveling Digestion

December 20, 2025 •

3 min read

Did you know that despite being a primary source of dietary sugar, the human body cannot absorb sucrose in its complex form? This disaccharide must be broken down first, a process managed by a highly specialized biological catalyst. This article explores the enzymatic reaction that converts sucrose into glucose and the key players involved in this fundamental process.

Quick Summary

The human digestive system uses the enzyme sucrase-isomaltase to break down sucrose into absorbable glucose and fructose. This process, called hydrolysis, occurs on the brush border of the small intestine, enabling the body to utilize the sugar for energy.

Key Points

Specific Enzyme: The human digestive system uses the enzyme sucrase-isomaltase to break down sucrose.
Location of Action: Sucrase-isomaltase is located in the brush border of the small intestine, where it acts directly on ingested sucrose.
Hydrolysis Process: The enzyme facilitates the hydrolysis of sucrose, a chemical reaction that uses water to split the disaccharide into two simpler sugars.
Resulting Monosaccharides: The breakdown of sucrose by sucrase yields one molecule of glucose and one molecule of fructose, both of which are readily absorbed.
Comparative Enzyme: In non-human organisms like yeast, a similar enzyme called invertase performs the same function but cleaves a different bond in the sucrose molecule.
Importance: Proper sucrase function is crucial for preventing the malabsorption of sucrose, which can lead to digestive issues associated with congenital sucrase-isomaltase deficiency (CSID).

The Core Enzymes: Sucrase and Invertase

To understand the conversion of sucrose, it's essential to recognize the two main enzymes responsible for this reaction, depending on the organism. In humans, the enzyme is specifically known as sucrase-isomaltase. In plants, fungi, and bees, a similar enzyme called invertase serves the same purpose. While both break down sucrose into glucose and fructose, they do so by cleaving different bonds within the sucrose molecule.

Sucrase-Isomaltase in Humans

In the human digestive tract, the primary enzyme for breaking down sucrose is sucrase-isomaltase. This is a double-function enzyme complex that resides in the brush border of the small intestine. The sucrase portion of this complex is what directly acts on sucrose. This enzyme is produced by intestinal cells. Its active site binds to sucrose and uses water (hydrolysis) to break the bond between glucose and fructose. The result is one molecule each of glucose and fructose, which are then absorbed into the bloodstream.

Invertase in Other Organisms

Found in sources like yeast, invertase also breaks down sucrose into glucose and fructose. It is used in the food industry to make invert sugar syrup and by bees to produce honey. Invertase cleaves a different bond in the sucrose molecule compared to human sucrase.

The Digestive Process in Humans

Carbohydrate digestion begins in the mouth and finishes in the small intestine. Here's how sucrose is processed:

Ingestion: Sucrose is consumed in various foods.
Stomach Bypass: Sucrose passes through the stomach without being significantly digested.
Arrival in Small Intestine: Sucrose reaches the brush border of the small intestine and encounters sucrase-isomaltase.
Hydrolysis: Sucrase-isomaltase quickly breaks down sucrose into glucose and fructose.
Absorption: Glucose and fructose are absorbed into the bloodstream for energy.

Comparison of Sucrase-Isomaltase and Invertase

Here's a table comparing sucrase-isomaltase (human) and invertase (from yeast):


Feature	Sucrase-Isomaltase (Humans)	Invertase (Yeast, Plants)
Primary Location	Brush border of the small intestine	Extracellularly in plants and microorganisms
Cleavage Point	Cleaves the O-C(glucose) bond	Cleaves the O-C(fructose) bond
Physiological Role	Digestion and absorption of sucrose and maltose	Transport, signaling, and osmoregulation; production of invert sugar
Resulting Products	Glucose and Fructose	Glucose and Fructose
Optimal pH	Slightly acidic to neutral (pH 6.0–7.0)	Acidic (pH 4.5) for optimal efficiency
Deficiency Condition	Congenital Sucrase-Isomaltase Deficiency (CSID)	Not applicable to humans; important for industrial purposes

The Consequences of Enzyme Deficiency

A lack of functional sucrase-isomaltase leads to Congenital Sucrase-Isomaltase Deficiency (CSID). Undigested sucrose ferments in the large intestine, causing gas and drawing water, which results in watery diarrhea. Symptoms include abdominal pain, bloating, gas, and diarrhea after eating sucrose. Severe cases can cause malnutrition and poor growth. Treatment options include a low-sucrose diet or enzyme replacement.

Conclusion

In summary, the enzyme in the human body that converts sucrose into glucose is sucrase, part of the sucrase-isomaltase complex in the small intestine. It uses hydrolysis to break down sucrose into absorbable glucose and fructose. A deficiency in this enzyme can cause CSID, highlighting its vital role in digestion. For more on the gene related to this enzyme, see the MedlinePlus Genetics page: https://medlineplus.gov/genetics/gene/si/.

Frequently Asked Questions

The primary function of the sucrase enzyme is to catalyze the hydrolysis of sucrose (table sugar) into its component simple sugars, glucose and fructose, during human digestion.

In humans, sucrase is found on the brush border, which consists of tiny, finger-like microvilli lining the cells of the small intestine.

While both enzymes break down sucrose into glucose and fructose, they differ in their origin and the specific bond they cleave. Human sucrase targets the bond on the glucose side, while invertase, common in yeast and plants, targets the bond on the fructose side.

A deficiency in sucrase, known as Congenital Sucrase-Isomaltase Deficiency (CSID), means sucrose is not properly digested. It is fermented by bacteria in the large intestine, causing symptoms like gas, bloating, cramps, and diarrhea.

No, the body cannot absorb the disaccharide sucrose directly. It must first be broken down into the monosaccharides glucose and fructose by the sucrase enzyme before it can be absorbed into the bloodstream.

After sucrase breaks down sucrose, the resulting glucose and fructose are absorbed through the wall of the small intestine and enter the bloodstream. They are then transported to cells throughout the body to be used for energy.

Congenital Sucrase-Isomaltase Deficiency (CSID) is considered a rare genetic disorder, though some patients with functional GI symptoms may have some level of sucrase malabsorption.