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Studies on Amino Acid Uptake by Ovine Small Intestine¹

Department of Animal Husbandry, Michigan State University, East Lansing, Michigan 48823

Mature mixed-breed ewes were used to study sites of maximum amino acid uptake and kinetic properties of neutral and basic amino acid transport systems in sheep small intestine. Uptake of 5 mM lysine increased with distance distal to the pylorus such that maximum uptake was obtained in the ileum. Distribution ratios (DR) (cpm per ml intracellular fluid/cpm per ml medium) for methionine and lysine, determined in an atmosphere of nitrogen or oxygen, indicated that intestinal transport was largely dependent on respiration-derived energy. Methionine DR determined after 60 minutes of incubation under nitrogen suggested that the methionine system(s) had some ability to utilize energy derived from substrate phosphorylation. Kinetic constants (K_m and V_max) were determined for methionine, glycine and lysine transport. The relative order of affinity by the amino acids for the transport site(s) (based on K_m data) was lysine > methionine > glycine. The relative order for rate of transport (based on K_m and V_max data) was methionine > Lysine > glycine. These results are similar to data published for the rat small intestine. Competition for binding between leucine and lysine was observed in sheep intestine. Saturating concentrations of leucine decreased lysine uptake by approximately 50%.

KEY WORDS: • amino acid transport • sheep • methionine • glycine • lysine • leucine lysine competition

¹ Michigan Agricultural Experiment Station Journal Article no. 6372. Supported in part by NIH Nutrition Training Grant GMO-1818.

² Ruminant Nutrition Laboratory.

Manuscript received 9 May 1973.

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