The uptake of naturally occurring amino acids by the plasma membrane of the human placenta.

The characteristics of the uptake of four naturally occurring amino acids, alanine, leucine, lysine and aspartate, by microvesicles prepared from the plasma membrane on the maternal surface of the human placenta were studied. Electron microscopy showed that a variety of fragments was interspersed between the vesicles and this heterogeneity probably accounted for the considerable variation in the results. Nevertheless, the properties of the uptake of amino acids were similar to those of vesicle preparations from other tissues. Insulin did not enhance the uptake of any of the amino acids.