Kinetic Characteristics of Glycine Transport by the Isolated Midgut of the Marine Shrimp, Penaeus Marginatus

Abstract

1. Mucosal glycine influx occurred via a single carrier-mediated, active transport entry process (Kt = 0·36 mM; Vmax=0·42 µmoles/g.min) with an absolute Na+ requirement. 2. Glycine transport inhibition by N2 gas, NaCN, NaN3, iodoacetate, 2,4-DNP, and ouabain was more extensive at 0·1 mM than at 1·0 mM glycine, suggesting a greater proportion of energy-dependent transport at lower amino acid concentrations. 3. Aliphatic neutral amino acids and histidine were more potent inhibitors of mucosal glycine influx than were aromatic neutral, and anionic amino acids. 4. Alanine was a fully non-competitive inhibitor of mucosal glycine entry, whereas proline appeared to be a fully competitive inhibitor of luminal glycine transfer. 5. D-Fructose added to the incubation medium restored normal glycine transport in the presence of alanine, indicating that the two amino acids most likely utilized separate, energy-consuming, mucosal transport processes. 6. A tentative model of glycine transport in the penaeid shrimp intestine is presented.