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Maltase is an informal name for a family of enzymes that catalyze the hydrolysis of disaccharide
maltose } Maltose ( or ), also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond. In the isomer isomaltose, the two glucose molecules are joined with an α(1→6) bond. Maltose is the tw ...
into two simple sugars of
glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...
. Maltases are found in plants, bacteria, yeast, humans, and other vertebrates. Digestion of starch requires six intestinal enzymes. Two of these enzymes are luminal endo-glucosidases named alpha-amylases. The other four enzymes have been identified as different maltases, exo-glucosidases bound to the luminal surface of enterocytes. Two of these maltase activities were associated with
sucrase-isomaltase Sucrase-isomaltase is a bifunctional glucosidase (sugar-digesting enzyme) located on the brush border of the small intestine, encoded by the human gene ''SI''. It is a dual-function enzyme with two GH31 domains, one serving as the isomaltase, the ...
(maltase Ib, maltase Ia). The other two maltases with no distinguishing characteristics were named maltase-glucoamylase (maltases II and III). The activities of these four maltases are also described as alpha-glucosidase because they all digest linear starch oligosaccharides to glucose.


Structure

Maltases are members of a group of intestinal enzymes called FamilyGH13 (
Glycoside hydrolase family 13 In molecular biology, glycoside hydrolase family 13 is a family of glycoside hydrolases. Glycoside hydrolases are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and ...
) that are responsible for breaking apart the α-glucosidase linkages of complex carbohydrates into simple to use glucose molecules. The glucose molecules would then be used as a sort of "food" for cells to produce energy (
Adenosine triphosphate Adenosine triphosphate (ATP) is a nucleoside triphosphate that provides energy to drive and support many processes in living cell (biology), cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known ...
) during
Cellular respiration Cellular respiration is the process of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cell ...
. The following are genes that can code for maltase: * Acid alpha-glucosidase which is coded on the GAA gene is essential to breakdown complex sugars called
Glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. It is the main storage form of glucose in the human body. Glycogen functions as one of three regularly used forms ...
into glucose. * Maltase-glucoamylase which is coded on the MGAM gene plays a role in the digestion of starches. It is due to this enzyme in humans that starches of plant origin are able to digested. *
Sucrase-isomaltase Sucrase-isomaltase is a bifunctional glucosidase (sugar-digesting enzyme) located on the brush border of the small intestine, encoded by the human gene ''SI''. It is a dual-function enzyme with two GH31 domains, one serving as the isomaltase, the ...
which is coded on the SI gene is essential for the digestion of carbohydrates including starch, sucrose and isomaltose. * Alpha-amylase 1 which is coded on the AMY1A gene is responsible of cleaving α-glucosidase linkages in oligosaccharides and polysaccharides in order to produce starches and glycogen for the previous enzymes to catalyze. Higher quantities of this gene in the brain have been shown to lower the risk of
Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...
.


Mechanism

The mechanism of all FamilyGH13 enzymes is to break a α-glucosidase linkage by hydrolyzing it. Maltase focuses on breaking apart maltose, a disaccharide that is a link between 2 units of glucose, at the α-(1->4) bond. The rate of hydrolysis is controlled by the size of the substrate (carbohydrate size).


Industrial applications

Alpha-amylase has an important function in degradation of starches, so it is used frequently in the baking industry. It is mostly used a means of flavor enhancing to improve bread quality. Without alpha-amylase, yeast would not be able to ferment. Maltose-glucoamylase is commonly used as a fermentation source as it is able to cut starch into maltose, which is then used for brewing beers and sake. Other than brewing, maltose glucoamylase has been studied by introducing specific inhibitors to stop the hydrolysis of the α-glucosidase linkages. By inhibiting the cleave of the linkages, scientists are hoping to devise a drug that is more efficient and less toxic to treating diabetes.


History

The history of maltase discovery began when Napoleon Bonaparte declared a continental blockade in his “Berlin decree” in 1806. This initiated the search for alternative sources of sugar. In 1833 French chemists Anselm Payen and Jean-Francois Persoz discovered a malt extract that converted starch into glucose which they called diastase at the time. In 1880, H.T. Brown discovered mucosal maltase activity and differentiated it from diastase, now called amylase. In the 1960s advances in protein chemistry allowed Arne Dahlqvist and Giorgio Semenza to fractionate and characterize small intestinal maltase activities. Both groups showed there were four major fractions of maltase activity that were intrinsic to two different peptide structures, sucrase-isomaltase and maltase-glucoamylase. Fifty years later entering the genomic age, cloning and sequencing of the mucosal starch hydrolase confirmed Dahlqvist and Semenza's findings.


Maltase deficiency

Acid maltase deficiency (AMD) also known as Pompe disease was first described by Dutch pathologist JC Pompe in 1932. AMD is a non sex linked autosomal recessive condition in which excessive accumulation of glycogen build up within lysosome vacuoles in nearly all types of cells all over the body. It is one of the more serious glycogen storage diseases affecting muscle tissue. AMD is categorized into three separate types based on the age of onset of symptoms in the affected individual. Infantile (Type a), childhood (Type b), and adulthood (Type c). The type of AMD is determined by the type of gene mutation localized on 17q23. Mutation type will determine production level of acid maltase. AMD is extremely fatal. Type a generally die of heart failure prior to age one. Type b die of respiratory failure between ages three to twenty-four. Type c die of respiratory failure 10–20 years of the onset of symptoms.


Comparative physiology

Vampire bats are the only vertebrates known to not exhibit intestinal maltase activity.


See also

* Maltase-glucoamylase *
Sucrase-isomaltase Sucrase-isomaltase is a bifunctional glucosidase (sugar-digesting enzyme) located on the brush border of the small intestine, encoded by the human gene ''SI''. It is a dual-function enzyme with two GH31 domains, one serving as the isomaltase, the ...


References


External links

*
Structure and evolution of the mammalian maltase-glucoamylase and sucrase-isomaltase
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