Α-Glucosidase
class of enzymes
α-Glucosidase (EC 3.2.1.20, (systematic name α-D-glucoside glucohydrolase) is a glucosidase located in the brush border of the small intestine that acts upon α(1→4) bonds:
Hydrolysis of terminal, non-reducing (1→4)-linked α-D-glucose residues with release of D-glucose
This is in contrast to EC 3.2.1.21 β-glucosidase.
Terminology
GO:0090599, the broad sense
The Gene Ontology entry GO:0090599 represents the broad sense of "alpha-glucosidase". It is defined as "catalysis of the hydrolysis of terminal, non-reducing alpha-linked alpha-D-glucose residue with release of alpha-D-glucose." In this sense, "alpha-glucosidase" can encompass a wide range of enzyme activities, differing by the linkage of their terminal (1→3, 1→4, or 1→6), the specific identity of their substrate (sucrose, maltose, or starch), among other aspects.
EC 3.2.1.20, the narrow sense
The definition associated with Enzyme Commission number 3.2.1.20 is narrower. It requires the linkage to be 1→4, and the preferred substrate to be smaller oligosaccharides (as opposed to larger polysaccharides like starch: alpha-amylase would otherwise be included). Human genes that produce enzymes with activities specified by this EC number include:
MGAM is the "maltase-glucoamylase", found on the intestine brush border.
GAA is the "acid alpha-glucosidase", found in the lysosome.
GANC, "neutral alpha-glucosidase C".
Synonyms mentioned by the Commission include maltase, glucoinvertase, glucosidosucrase, maltase-glucoamylase, α-glucopyranosidase, glucosidoinvertase, α-D-glucosidase, α-glucoside hydrolase, α-1,4-glucosidase, α-D-glucoside glucohydrolase. These names are not recommended because they may only refer to a specific activity of the enzyme, or a specific protein having this acvitity.
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