Na+-dependent uptake of 4-azidophenylalanine by pig intestinal microvillus vesicles. Interaction with neutral amino acid uptake and labelling pattern.

A procedure for the synthesis of tritiated 4-azidophenylalanine in a radioactively homogeneous form is described. The characteristics of the 4-azidophenylalanine uptake by pig intestinal microvillar vesicles and its interaction with the neutral amino acid transport have been studied. 4-Azidophenylalanine is transported into an osmotically sensitive space and the transport is sodium dependent. It is demonstrated that 4-azidophenylalanine transport is inhibited by L-alanine and L-phenylalanine but not by L-lysine and D-glucose. Likewise 4-azidophenylalanine inhibited the initial transport of L-alanine and L-phenylalanine but the initial transport of L-lysine and D-glucose was unaffected. Treatment of microvillar vesicles with 4-azidophenylalanine in combination with photolysis irreversibly inactivated the L-alanine transport. Photolabelling in the presence of sodium using tritiated 4-azidophenylalanine resulted in labelling of 10 peptides, all found in the fraction insoluble in Triton X-100. Omission of sodium from the reaction mixture or addition of L-alanine did not specifically abolish labelling in any of the labelled components.