Alkaline lipase in rat intestinal mucosa: physiological parameters

Area of Science:

• Gastroenterology
• Biochemistry
• Enzymology

Background:

• The rat intestinal mucosa possesses various enzymes crucial for nutrient digestion and absorption.
• Lipases are key enzymes in lipid metabolism, hydrolyzing triglycerides into fatty acids and glycerol.
• Understanding the specific roles and localizations of intestinal lipases is vital for comprehending fat absorption.

Purpose of the Study:

• To characterize an alkaline lipase present in the rat intestinal mucosa.
• To determine the enzyme's subcellular localization and optimal activity conditions.
• To investigate the enzyme's role in dietary fat metabolism within the intestinal lining.

Main Methods:

• Alkaline lipase activity was quantified using a glyceryl tri[14C]oleate emulsion assay at pH 8.0.
• Subcellular fractions of mucosal homogenates were isolated via differential centrifugation.
• Intestinal cells were sequentially isolated from villus to crypt using citrate and EDTA buffers.

Main Results:

• The alkaline lipase exhibited peak activity in the proximal intestinal quarter and villus tips.
• The majority of lipase activity was localized to the cytosolic fraction.
• Enzyme activity was significantly enhanced (threefold) by bile salts, with Ca2+ and taurocholate being essential for optimal function.
• Intraduodenal infusion of glyceryl trioleate reduced mucosal activity, which was restored by phosphatidylcholine co-administration.

Conclusions:

• The rat intestinal mucosal alkaline lipase is primarily located in the cytosol of villus tip cells in the proximal intestine.
• Its activity is modulated by bile salts and essential cofactors, suggesting a role in luminal fat digestion.
• The findings indicate this lipase is important for mucosal glyceryltrioleate metabolism, potentially aiding in fatty acid absorption.