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Acidic mammalian chitinase is a proteases-resistant glycosidase in mouse digestive system

View Article: PubMed Central - PubMed

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.

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Related in: MedlinePlus

Expression, localization and activity of pepsin C and AMCase in mouse stomach.(a) The mRNA levels of nine genes were quantified by qPCR. Upper panel, actual value; lower panel, logarithmic scale. Y axis represents molecules per 10 ng of total RNA. The numbers in the figure indicate relative expression levels with GAPDH set at 1.0. Pep C, pepsinogen C; Gif, gastric intrinsic factor; ATPase, H+/K+-ATPase. (b) Expression and co-localization of pepsin C and AMCase proteins in mouse stomach sections shown by immunohistochemistry using anti-pepsin C (green) and anti-human AMCase (red). Scale bars, 1,000 μm (upper panels); 50 μm (lower panels). (c) pH profile of pepsin and AMCase. Values in (a) and (c) represent mean ± SD. **p < 0.01. P-values were determined using Student’s t-test.
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f2: Expression, localization and activity of pepsin C and AMCase in mouse stomach.(a) The mRNA levels of nine genes were quantified by qPCR. Upper panel, actual value; lower panel, logarithmic scale. Y axis represents molecules per 10 ng of total RNA. The numbers in the figure indicate relative expression levels with GAPDH set at 1.0. Pep C, pepsinogen C; Gif, gastric intrinsic factor; ATPase, H+/K+-ATPase. (b) Expression and co-localization of pepsin C and AMCase proteins in mouse stomach sections shown by immunohistochemistry using anti-pepsin C (green) and anti-human AMCase (red). Scale bars, 1,000 μm (upper panels); 50 μm (lower panels). (c) pH profile of pepsin and AMCase. Values in (a) and (c) represent mean ± SD. **p < 0.01. P-values were determined using Student’s t-test.

Mentions: In stomach, number of gastric mucosa proteins, such as gastric intrinsic factor31, mucin32, gastrin33 and H+/K+-ATPase34, are synthesized by various glandular cells. We compared the expression levels of AMCase mRNA with those of the gastric mucosa proteins and housekeeping genes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and β-actin, using our previously reported quantitative PCR system2627. We found that AMCase was the second most abundantly expressed molecule in the stomach tissue being exceeded only by pepsinogen C and its level was significantly higher those of Chit1 and other tested gastric mucosa and housekeeping genes mRNAs (Fig. 2a). These results indicate that AMCase is a major transcript in the mouse stomach.


Acidic mammalian chitinase is a proteases-resistant glycosidase in mouse digestive system
Expression, localization and activity of pepsin C and AMCase in mouse stomach.(a) The mRNA levels of nine genes were quantified by qPCR. Upper panel, actual value; lower panel, logarithmic scale. Y axis represents molecules per 10 ng of total RNA. The numbers in the figure indicate relative expression levels with GAPDH set at 1.0. Pep C, pepsinogen C; Gif, gastric intrinsic factor; ATPase, H+/K+-ATPase. (b) Expression and co-localization of pepsin C and AMCase proteins in mouse stomach sections shown by immunohistochemistry using anti-pepsin C (green) and anti-human AMCase (red). Scale bars, 1,000 μm (upper panels); 50 μm (lower panels). (c) pH profile of pepsin and AMCase. Values in (a) and (c) represent mean ± SD. **p < 0.01. P-values were determined using Student’s t-test.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5121897&req=5

f2: Expression, localization and activity of pepsin C and AMCase in mouse stomach.(a) The mRNA levels of nine genes were quantified by qPCR. Upper panel, actual value; lower panel, logarithmic scale. Y axis represents molecules per 10 ng of total RNA. The numbers in the figure indicate relative expression levels with GAPDH set at 1.0. Pep C, pepsinogen C; Gif, gastric intrinsic factor; ATPase, H+/K+-ATPase. (b) Expression and co-localization of pepsin C and AMCase proteins in mouse stomach sections shown by immunohistochemistry using anti-pepsin C (green) and anti-human AMCase (red). Scale bars, 1,000 μm (upper panels); 50 μm (lower panels). (c) pH profile of pepsin and AMCase. Values in (a) and (c) represent mean ± SD. **p < 0.01. P-values were determined using Student’s t-test.
Mentions: In stomach, number of gastric mucosa proteins, such as gastric intrinsic factor31, mucin32, gastrin33 and H+/K+-ATPase34, are synthesized by various glandular cells. We compared the expression levels of AMCase mRNA with those of the gastric mucosa proteins and housekeeping genes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and β-actin, using our previously reported quantitative PCR system2627. We found that AMCase was the second most abundantly expressed molecule in the stomach tissue being exceeded only by pepsinogen C and its level was significantly higher those of Chit1 and other tested gastric mucosa and housekeeping genes mRNAs (Fig. 2a). These results indicate that AMCase is a major transcript in the mouse stomach.

View Article: PubMed Central - PubMed

ABSTRACT

Chitinases are enzymes that hydrolyze chitin, a polymer of &beta;-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.

No MeSH data available.


Related in: MedlinePlus