ASAS Western Section Abstract
Effects of hydrolysable tannin on the activities of porcine jejunal enterocyte brush border membrane-bound alkaline phosphatase (EC 220.127.116.11), aminopeptidase N (EC 18.104.22.168), and sucrase (EC 22.214.171.124) were examined. Jejunal mucosa was scraped from three 26-kg pigs and enterocyte brush border membrane vesicles, with an average enrichment of 21-fold in sucrase specific activity, were prepared by Mg2+-precipitation and differential centrifugation. The brush border membrane vesicles were treated with tannin by mixing 100 uL (1 mg protein) batches of vesicle suspension with 20 uL of vesicle resuspension buffers containing increasing amounts of the tannin to achieve the treatment concentration gradients (0, .05, .10, .25, .50, 1.00, and 2.50%). The mixture (120 uL) was incubated at 4°C for 60 min and was then diluted to contain .25 mg protein/mL prior to enzyme assays. P-Nitrophenyl phosphate (2 mM), L-alanine-P-nitroanilide hydrochloride (28 mM), and sucrose (28 mM) were respectively used in alkaline phosphatase, aminopeptidase N, and sucrase assays (37°C). All enzyme assays were conducted under the conditions of linear enzyme reaction. Inhibition kinetics were analyzed according to Michaelis-Menten equation. As a percentage fraction of the control (no tannin), the maximal inhibition of enzyme activity (Imax) was 24.4% for alkaline phosphatase, 54.8% for aminopeptidase N, and 61.2% for sucrase (P < .05). These results imply that the adverse effects of extractable polyphenols in feeds on the digestive utilization of dietary carbohydrates and proteins in the pig are partly due to their direct interference with the normal functions of the small intestinal brush border membrane-bound digestive enzymes.
Key words: Tannin, Jejunal brush border enzymes, Pigs
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Prepared for the web 5-26-97.