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Retinyl ester hydrolytic activity associated with human intestinal brush border membranes
K M Rigtrup1, L R McEwen, H M Said
1Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN.
The American Journal of Clinical Nutrition
|July 1, 1994
Summary
Human and rat small intestine brush border membranes (BBMs) possess distinct esterase activities crucial for vitamin A absorption. These enzymes efficiently hydrolyze retinyl esters, supporting the rat as a valid model for human vitamin A metabolism.
Area of Science:
- Biochemistry
- Human Physiology
- Nutritional Science
Background:
- Absorption of vitamin A requires hydrolysis of retinyl esters in the small intestine.
- Previous studies identified distinct esterases in rat brush border membranes (BBMs) for short- and long-chain fatty acyl retinyl esters.
Purpose of the Study:
- To investigate and characterize retinyl ester hydrolytic activities in human BBMs.
- To compare these activities with those previously observed in rat BBMs.
Main Methods:
- Preparation and biochemical analysis of human and rat BBMs.
- Enzyme kinetic studies using various retinyl esters (e.g., retinyl palmitate, retinyl caproate, retinyl butyrate).
- Assessment of bile salt stimulation (deoxycholate, taurocholate).
Main Results:
- Human BBMs exhibit distinct hydrolytic activities for short- and long-chain retinyl esters, similar to rat BBMs.
- Long-chain ester hydrolysis was optimally stimulated by deoxycholate (dihydroxy bile salt).
- Short-chain ester hydrolysis was optimally stimulated by taurocholate (trihydroxy bile salt), with potential evidence for two separate short-chain activities.
Conclusions:
- Human and rat BBMs share similar retinyl esterase activities, suggesting the rat is a suitable model for studying vitamin A absorption.
- The differential stimulation by bile salts and distinct kinetic properties (KM values) support the presence of multiple esterase activities in BBMs.