Most digestive enzymes produced by the small-intestinal wall are bound to the apical (brush-border) cell membrane of intestinal epithelial cells rather than being freely secreted into the intestinal lumen.

Verified by Lenz · Jun 1, 2026

The Short Version

The evidence supports the core claim: small-intestinal digestive enzymes are predominantly brush-border membrane proteins, especially disaccharidases and many peptidases. A minor fraction can be shed into the lumen, and not every enzyme in intestinal cells is brush-border bound, but those caveats do not overturn the main point.

Caveats

Some brush-border enzymes can be released into the lumen by proteolytic cleavage or membrane vesicle shedding, so the statement is not absolute.
The claim is strongest for classic terminal digestive hydrolases such as disaccharidases and many peptidases, not every enzyme present in intestinal mucosal cells.
Some educational sources use "secreted" loosely for enzymes delivered to or acting at the epithelial surface, which can blur the distinction between membrane-bound and freely luminal enzymes.

The Receipts

Small Intestine - PMC - NIH
PMC (NIH)Apr 23, 2020
Disaccharidase-deficient animals have normal ultrastructure of intestinal villi and brush-border membrane
PubMedNov 1, 1981
Intestinal brush border revisited
PMC (NIH)Oct 16, 2003
Chapter 16 Production and gene expression of brush border ...
PMCApr 20, 2020
Sucrase-isomaltase: structure, biosynthesis and post-translational modifications
PubMedFeb 1, 2013
Intestinal disaccharidases and brush-border membrane defects
PubMedAug 1, 2019
Aminopeptidases of the intestinal brush border: structure and function
PubMedMar 1, 2019
Physiology of Intestinal Absorption and Secretion
PubMed Central (NIH)Jul 1, 2016
Longitudinal study of the human intestinal brush border membrane proteins. Distribution of the main disaccharidases and peptidases
PubMedOct 1, 1983
Brush border membrane peptidases in the human small intestine
PubMedApr 1, 2001

+ 11 more sources — see the full list on Lenz

Filed Under

Brush BorderIntestinal Epithelial CellsSmall Intestine

Most digestive enzymes produced by the small-intestinal wall are bound to the apical (brush-border) cell membrane of intestinal epithelial cells rather than being freely secreted into the intestinal lumen.

The Short Version

Caveats

The Receipts

Filed Under

More Fact Checks

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