Abstract
Chitinases are enzymes that hydrolyze chitin, a polymer of β-1, 4-linked N-acetyl-D-glucosamine (GlcNAc). Chitin has long been considered as a source of dietary fiber that is not digested in the mammalian digestive system. Here, we provide evidence that acidic mammalian chitinase (AMCase) can function as a major digestive enzyme that constitutively degrades chitin substrates and produces (GlcNAc)2 fragments in the mouse gastrointestinal environment. AMCase was resistant to endogenous pepsin C digestion and remained active in the mouse stomach extract at pH 2.0. The AMCase mRNA levels were much higher than those of four major gastric proteins and two housekeeping genes and comparable to the level of pepsinogen C in the mouse stomach tissues. Furthermore, AMCase was expressed in the gastric pepsinogen-synthesizing chief cells. The enzyme was also stable and active in the presence of trypsin and chymotrypsin at pH 7.6, where pepsin C was completely degraded. Mouse AMCase degraded polymeric colloidal and crystalline chitin substrates in the gastrointestinal environments in presence of the proteolytic enzymes. Thus, AMCase can function as a protease-resistant major glycosidase under the conditions of stomach and intestine and degrade chitin substrates to produce (GlcNAc)2, a source of carbon, nitrogen and energy.
Highlights
Murine AMCase is most active at pH of around 28,23–25
The results clearly indicate that the pepsin-resistant 41 kDa band represents CatD25 and the resulting chitin-binding domain (CBD) was degraded by pepsin suggesting that, in contrast to other soluble proteins, AMCase is stable in the presence of pepsin C at pH 2.0, even though it is partly cleaved, releasing the catalytic domain (CatD) fragment
We show that AMCase is resistant to proteolytic activity of pepsin C at pH 2.0 as well as trypsin and chymotrypsin at pH 7.6 and retains its chitinolytic ability under both conditions
Summary
Murine AMCase is most active at pH of around 28,23–25. Mouse stomach produces large quantities of AMCase mRNA and protein[26,27]. AMCase seems to function as a digestive enzyme that breaks down chitin-containing ingested material in mouse stomach. It has not been known whether it has this role www.nature.com/scientificreports/. Values in (b) and (d) represent mean ±SD from a single experiment conducted in triplicate. We show that AMCase is a major chitinase in stomach resistant to pepsin and trypsin/chymotrypsin digestion and that it can function as a digestive enzyme under conditions in other parts of GIT
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